Love this thread!
I think a shaft drive car would be brilliant for todays stock classes (21.5t boosted or 17.5 blinky), the torque effect of the motor is much reduced from the old brushed days, a shaft car would give you excellent accleration.
I have been looking for an older car to update for a while, the trouble is (in my opinion) you need to have one that you can use a spool in (with replaceable outputs) and a gear diff.
The only gear diff for a shaft car that i can find is one by SPecR for the Tamiya TB03 so i have been slowly collecting parts for that car, they are still readily available and you can also use the same suspenion components as the 417...so I don't know if its really considered an 'old car'....
I also have some Yokomo SD parts lying about so might do something with those too. Someone was asking about SD parts on here, to get all the SD/CGM parts you need to go to Japan (RC Race & Drift or Banzai) as the SD is still used as a drift car, about 99% of all the parts are still available...plus some new parts that the latest drift car uses.
A Tamiya 414M2 would be my ideal 'old car', but they are tough to find...anyone have one they want shifting