I installed the v3 GB in my Sherman 76, and now have a better idea of things. Some observations from a relatively newbie, and in some cases just my personal opinion...
The adapter plates are mounted with the six "self-tapping" screws that held down the old stock GBs, they are reused. The same holes are used. While the plates are a little thicker than the stock GB mount thickness, there is enough length for the screws to mount, and the plates are also held by a couple of locator pins. There are three taped bosses on each plate; two each will be used to mount the new GB with regular bolts. I thought the third boss would be used, but I can't see any mount hole through the gears for it. You need only four bolts, so the eight supplied is enough- I was wrong in thinking 12 were needed. See pic.
GBs barely fits. The tabs on motors have to be bent down about as far as possible. Even then, the insulation (but not bare wire) of red/black wires touches the opposite GB face, which is painted black. The black wire from right motor GB interferes just a tad with lifting up left rear GB dust cover, I have to twist cover and right GB housing away from each other to uncover gears left side. I may file down the plastic cover edge a bit. Right rear cover no prob. Nothing is shorting though.
I haven't tried removing the forward dust covers(printed with "TAIGEN") with the triangular "tranny cover" in place. I don't believe it is possible. They don't touch the tranny cover, but there is not any room to get in there to lift them off.
I ran it for only ten minutes outside, so bear that in mind, and my "newbie" thoughts:
Just the improvement I wanted over the stock 3:1 GB. Lots of control, I can start crawling, or go at a reasonable top speed. Good low end. It creeps easily, and I went up a 12% grade creeping barely moving. At full speed up incline tracks slip a bit, but that's not abnormal. Very LOUD, the gears make a racket. My personal feel on it is that this would be a good speed range for controlling a Sherman 76 tank, but my guess is I would want to leave my Tiger metal with it's stock 4:1 390.
Right plate attached with reused tapping screws, note threaded bosses in left plate.
Left gearbox packed with gears, dust covers removed. Right GB covers installed. Both GBs installed.
Sherman re-assembled. Wires touch opposite GB even with tabs bent fully; left rear dust cover has to squeeze by right motor's black wire to open. Front dust covers probably can't be removed with tranny cover on.