Hope to have it wired up soon.
Found a simple way to use standard 64p spur gears.
72t will not clear the diff backing plates, 78t fits fine.
Standard 12th rear wheels fit, but maintaining ride height will require larger diameter tires than most 12th scale cars run, Tamiya apparently wanted this car to run 52-45mm tires, try much smaller than that and the chassis will run out of clearance.
Options I see are to use Tamiya RM-01 foams, or F1 foams.
Full size Jaco Rear tires will work, just...
To check max rollout, that's a 78x55 gear for 116+mm roll and stock 52.5mm tires.
Gear selection shouldn't be an issue for 17.5 blinky 1s where 85-110mm roll are the average over a broad range of motors and tracks.