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The problem with racing that is it isn't going to be competitive against a more modern TZ750, with a modern frame... and tires... and wheels... and brakes... and cartridge forks....

Looks cool though

$35,000
Who says prices are depressed?

If it's already been welded, you need someone that actually knows what their doing to try to rebuild it.
It MAY have been welded because "Racebro thought he was dealing with a 100hp bike or something,..." OR it was welded because it was loose when it was last taken apart.
We were talking about what press to use... when I take them apart, I find they take (IIRC) 5-7 tons to press them apart, and they POP when they come apart... That's a good one that can be pressed together. Then OTHER ones take a couple of tons and just kinda smooosh apart... THAT one gets welded.
If done right, just grind out the weld, and start again. There shouldn't be GOBS of weld, you only need a tack or two.
I have often said that anyone with a brain and a press can rebuild cranks... then I saw some of the abortions done... so I have to retract that statement. I have seen new, aftermarket cranks that had to be trued. Rebuilding cranks is simple, but kinda finicky... I guess it takes practice.
Use stock RD400 pins, they're serrated, so they hold better. Wiseco makes hollow pins if you're doing a performance motor. Wiseco and Suzuki offer silvered big end bearings. ProX rod have a split big end, like the TZ rod, that oils better... again IIRC (I don't do a lot of RD350s, I'm a TZ or RD400 guy)

The first time I saw that frame I had to have one.
Got in touch with my good friend Denis Curtis, of CMR fame, to build me one.

So as it turns out: they couldn't keep rings in the thing. The frame set up a sympathetic vibration in the motor that made the rings flutter. If the rings lasted the whole race, the bike probably won, but the bike dropped out of a lot of races with ring/piston failure.
... and that's why they only made a couple of them. Coolest LOOKING TZ frame out there

1975 King Kenny won the Indy mile (dirt) on a TZ750.
At the end of the race Chris Economaki rushed through the crowd for his comments, Chris pushed the mic into Kenny's face and King Kenny said to the world "They don't pay me enough to ride that thing".
... and the bike was banned.

What I have a problem with, being Canadian, is the later, '85 and newer, Canadian model RZ is a better bike but nobody wants them. A mint, mint '89 sells for $10,000 CDN, to a Canadian, Americans don't want them.

$27 grand for a '84 RZ is stupid. I have a TZ350B in better shape than that RZ and there isn't a hope in hell I could get $27 grand for it. They made 4200 TX250/350Bs and they made a bazillion '84 RZs. I think the seller did better than the buyer. That bike was "well sold".

They're as reliable as any true racer can be... they're 2T so there isn't a lot to go wrong.
There are pattern parts available for MOST stuff. Cases are unobtainium. They don't really share any parts with street bikes. Cylinders can be nikosil'ed (they're chrome stock). The cranks are rebuildable. The bearings are "off the shelf". I think Nova does a transmission.

I have a fleet of TZ250/350s and have no problem keeping them going... I have also been collecting TZ parts forever.
Obtaining a TZ750 isn't easy or cheap. A TZ250/350 is easier to ride, easier to keep going and in comparison CHEAP ... AND it still is competitive (because of the TZ750's relative rarity at vintage race meets, they get lumped into classes where they don't stand a chance.
If you go to vintage meets in western US try to find Dave Crussel... nice guy, knows more about TZ750s than most.
CMR racing did a TZ750 frame... if you want one it could probably be arranged (I know a guy).
The TZ750 was a seminal bike... they kinda suck now... history marching on and all. I've not owned one, but have worked on lots of them. They are not a "fun" bike to ride. I might know of one for sale in Canada.

Internet gossip says there is someone working on a custom cased TZ750 with 4 Whampus jugs, that is rumoured to put out 250HP all day long, that Dave Crussel is supposed to ride.

A decent 520 chain will have no problem with the "higher power" of your RD.
A modern 520 has more tensile strength than the stock POS 530 chain.
I run a 520 on a GS1000 racer with twice the HP and almost twice the weight of your RD
The TZ250/350's of the day ran a 520 chain and the sprockets are drop in to a RD... the RZ front sprockets fit too. IIRC the Daytona rears are different, I think you use XT/TT rear sprockets

We will NOT speak of the mess the swingarms are

The stock ones are nothing more than bling.

Less than BLING, the ones I got had a combustion chamber of 27-28cc's... so you're pretty assured of losing HP... it's easier to make stock heads work

I use the brightly colored ones, from the computer trade, when "prototyping" wiring. Use them to hold the wiring in place till it's done. (If you've done BIG wiring jobs, you find yourself 3/4 ways done, only to find you're routed it wrong).
When you're done, replace all the brightly colored straps with whatever you are using permanently
Been doing that for years and years

[PROBLEM]

Calculate your theoretical compression, to see if you're in hi-test gas territory... AND compression adds to timing, adding more compression acts like adding timing... and modern gas is much better than 1975 gas, and needs/wants less timing
Whacked squish can make it ping... ping at idle is a PROBLEM

It's shouldn't be a "points" issue... timing: maybe. I'd try setting the timing at 1.6-1.7mm BTDC and see what that does

UV light kills them, the cover only last a couple of years. Put a tarp over it and it lasts forever. They will take a surprising amount of wind load... do you get tornadoes where you live?

Your local bearing house will have several bearings at several price points, all well below any "dealer" price. Seals too. Being a motorcycle wheel bearing isn't terribly taxing... the cheapest bearing you can find will be fine (as long as you buy it it at a bearing house. DO NOT buy bearings off Amazon or Aliexpress).

Mr. SoCal: why do you want C3 bearings in a wheel?

Too bad it's in Canada.

If anyone want's it, he is local to me.