Someone's had the same idea as me. Beaten me to it as well
Yes, the bigTrak is an interesting platform to convert, though a bit dated. I had considered it as well but ended up going with a more current base platform that uses tank treads instead of wheels.
That's right. 2 square magnets in each side of the gear box. 1 side also has a dead reconing IR in there too.
Cool. I had a Big Trak when I was a kid. I wish I still had it!
I recall that the left and right drive wheels were loosely coupled with a magnet. This helped ensure that BigTrak drove straight when going forward and backward. The motors were strong enough to overcome the magnetic force when commanded to turn in opposite directions, so it could turn.