Looking at options for my 1977 RD400C. Not a stock rebuild but a custom Steve baker replica with seat/tank/swingarm from CMR Racing, R6S 43mm forks, etc....
Dyna S or Vape?
Pros and cons for each?
Vape, or even an HPI system. That way you replace the entire charging and ignition system with something modern. The spark on my vape is huge, never fouled a plug, unlike my stock points bike.
I'd definitely go for VAPE or HPI. Both are significantly lighter than the OEM stator/rotor/regulator/rectifier/coil system. And can be run without a battery. If no battery, the total weight savings is at least 10 lbs, if not more.
The VAPE has more lighting power available as well, an 80/100 w H4 headlight bulb is no problem. No carbon brushes to wear out.
Also, the VAPE rotor is lighter, and sitting closer to the LH main bearing. Which gives less stress on the crank. The trigger geometry is way better than points, and also better than a Dyna Or other electronic trigger located where the points were. This gives more stable timing, as crankshaft dynamics at high rpm will cause bending oscillations at the far end, where the points cam is located.
if you're going super minimalist, go hpi. also has a built in curve that works really well and is super light.
Street bike or racer?
This is for a street bike so being able to run without a bettery, yet still power lights is a plus. How tricky to install the VAPE setup? Who sells the HPI setup?
vape is sold by economy cycle. HPI can be had at treatland
https://www.economycycle.com/shop/yamaha-rd250350400r5ds6ds7-parts/electrical-ignitions-lighting/ignition/mzb-cdi-electronic-igntion-for-yamaha-rd250350400r5ds7-street-version/
there is a forum discount coed at economy, its 2sw.
https://www.treatland.tv/HPI-CDI-mini-rotor-ignition-system-yamaha-RD350-p/hpi-yamaha-rd350-mini-rotor.htm
bens a great guy to deal with as well.
Plenty of info in the 'team scream' section below on install.