hello
My diff has two sets of angle grinder gears (5" grinder) the big gears are used as side gears and the small ones as pinions. The small gears run on the 5/16" bolt you can see through the barrel in the center of the drive. The output shafts are 5/8" allen head bolts. The front wheel axles are also 5/8" allen head bolts machined down to 20 mm. The drive shafts are the 1/2" allen wrenchs with the short arm cut off so they are effectively 1/2" HARD hex shafts. I put a small spring in the diff end socket to keep the ball end at the wheel fully engaged. there may be some change in drive shaft length but it is accomodated by the two socket head bolts.
My electric drive is 36v 500w with 3 7ah batteries to keep the weight down (it's not enough battery though, 10 ah would be much better! or lithium ion)
Ed