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Hi tops were popular for a time and I always figured the reason was that OEM slides were longer, so in power restricted markets they fitted low tops to prevent full throttle and in other markets hi tops and long slides allow full throttle.

Long slides can be carefully shortened or replaced to work with low tops.

So hi top slides and hi tops should be the same as low tops with short slides functionally.  The rest is basic tuning.

Vintage bikes I use the clutch, modern bikes no clutch up and down the box.

Not on a GT750.  Tacho and water pump are from a gear on the crank to a train of gears and then a cross shaft to the water pump.  No clutch involved.  As long as the motor turns, so do all the rotating bits.

You looking for a GT750 cafe racer/restomod project?  I happen to have one with TL1000 suspension and wheels and a GusKhun tank and seat.  Choice of Bassani or J&R Power pipes.  I just started on it, so lots of room for personal touches 

#284 series IIRC.  I like them.  LEDAR made similar needle jets back in the day.  I had a pair in an RD400D a couple of decades back.

For upshifts, back off the throttle small amount to unload the gears and snick it up to the next one. Downshifts take more finesse and not recommended for situations where there's traffic. Just jam on the brakes, pull in the clutch and drop down as many gears as you need to.  Brakes are made for braking, clutches and two stroke motors, not so much.

For the drag strip us a CO2 bottle, solenoid and ram and it will up shift at WOT for as many shifts as there's gas in the bottle. We use the horn button to shift BUT if you need to use the horn, you will upshift instead.  There's not enough time to flip the horn/shift switch and then hit the horn.

Again for upshifts you could use what's known as a window switch that activates the air shifter at certain RPM but to short shift you have to hit the button or back out of the throttle.

If/when your thumb gets worse take a look at Pingel electric shifter that can shift up and down and fit a button in the space that a starter button would be on a 4 stroke.

Not sure about borrowing someone's vibrator, but tapping the brake line with a wrench or screwdriver usually helps to dislodge air bubbles so they can rise.

Another thing to check is the caliper mounts.  It is common on RDs for the caliper to mount out of square.  Simple check is to loosen the caliper mounting bolts so the caliper can move easily and then try the brake lever, if it's not firm, slowly tighten one mounting bolt and watch the caliper as you squeeze the lever.  You should be able to see it flex as the pads try to grip the disk.

Shim the gap between caliper and fork leg as required to get it to fit square.

double check fuel level and pilot circuit.

I'll have to make a couple bowl drain adapter screws for checking actual fuel level. .....

Good idea to check fuel level. 

We all know that checking float height is just a simple way to do that but in the real world it's not as accurate and doesn't identify issues such as floats hanging up or float needle jets not sealing.  When there are carb problems, I always take the extra time to check the actual fuel levels and it's surprising how often it helps to identify an issue that is invisible with a simple float check.

Choke plungers seem to last forever, but they do in fact go hard and fail to seal properly.

If the seal end is hard or doesn't seal well, replace them.  I had that issue on a GT750 a while back with a plunger that failed to seal properly and ran really rich on that cylinder.  RD400 has one plunger and a cross connector, so it's a cheap fix if that's the issue.

That's a nice looking LC, but first gear must be a PIA to ride. Early 750 top end is really tame and easy to ride if it sits on top on a 400 transmission.

Fondseca had dry clutch covers with kickstarter boss and long input shaft to take 400 gears.  Our RD350 has RD crankcases and wet clutch, TZ350 crank, TZ750 top end and clutch cover modified to accept a TZ water pump. 

I just bought an LED 1157 from my local auto parts store - remember them? and the brake light is much brighter than the rear (running) light.

Better to support your local parts store or dealer IMHO.  Jeff Bezos doesn't need my cash, so I try to avoid making him take it. Besides, It's nice to take home shiny things instead of waiting for the truck to arrive.

Last RD350 I repaired came in with JL pipes.  They are gorgeous and sound great and make great power.  Admittedly I spent time running simulations on different port specs to match the pipes.  Loved those pipes on that bike.

My own RZ350 came with Spec2 pipes and they are really sweet.  also a great sound and nice powerband, but with stock porting perhaps slightly less manic than the JLs. 

If someone was to buy a box load of different pipes and run them on a few sets of different port configurations, I'd love to see the results.

10.4 is good, 133 is a nice number.  What do his 60 foot times look like? 

I tried that an it's really hard to read the plugs after a 1/4 mile run. Are you running leaded or unleaded race gas?  The colors are very different.

I need to buy /build a spare rear wheel so I can strap it to a dyno and get the jetting right.  To do that I also need to take accurate notes and record EGT as well as power/torque and A:F.  Then I can adjust jetting at the track based on changes in RAD compared to the dyno runs and use EGT as a check.

I once tried to use an A:F meter and other instrumentation at the drag strip which is a waste of time unless you can make sense of that data as you watch for the tacho to bounce or the shift light to come on.  Above my pay grade.  It works with a data logger, but I have come to believe that dyno time is the most important investment.

Not that the bike is in any way similar to yours but I'm running #310 in VM34s on a TZ700 (40900) top end with Blaster reeds and open stingers (no mufflers).

Aftermarket poarts are often manufactured to fit a number of models and often include wires and functions not applicable to your make/model.  For example Yamaha may have fitted a similar looking switch to say RD400 and XS400 and the XS would have a start button and internal wiring that may not be the same as the RD.

The OEM design would be slightly different for each bike but aftermarket may be one switch offered for both, and that's where you have to plot each wire combination to work out what's what. 

I recently bough switches for an early Honda and they included indicators and front brake switch that were not fitted prior to about 1968 ish, so you may have to do some detective work or get more accurate repops from John at Economy.

Yellow/red is typically starter solenoid which might be useful on some older Yamahas but not on an RD400.

But if you add in a modern ignition, additional functions, LED headlamp and modern solid state R/R, all with non OEM colors, you can drive yourself certifiably mad.  Think of it as a challenge.

Can't you just swap the two stock fork legs around so that the caliper moves from in front of one side to behind on the other side?  Or is that too easy?

That's a nice piece, but can't you just use a stock GT750 cover?  I have a brand spanking new (NOS) one here looking for a new home.  Yours in exchange for a small pile of drink vouchers.

Not exactly obsessing, but I'd really like to get another GMC Safari.

Seriously.  Years ago, my in laws bought one cheaply with a lot of miles on it.  When we moved them from Oregon to Illinois, I loaded their old van up with their stuff and drove it across from the west coast and it already had 194,000 miles on it.  It was rough and old and ugly, so I felt at home in it...

After replacing a lot of electrical items and storing the middle and rear row seats in the shop, it carried race bikes all over the place. FZR400 for chassis straitening.  Throw it in the back.  GT750 Suzuki to the dyno to test different pipes. Check. 8x4 plywood sheets. check.  Drywall. Check.

It finally passed its use by date with another 130,000 or so miles on the clock and the motor still ran strongly and it shifted gears fine until it blew a transfer case.  I tried to sell it but it was worth more as scrap steel.  If I could get another but with a V8 motor and new suspension, I'd be interested. 

It's a mid sized awd van with huge carrying capcity.