I dont know how many times per week I can post this...
The 1g puts the roll stoppers (front/rear motor mounts) on the block, and the 2g puts them on the tranny. So a 2g tranny could work in a 1g, the mounts on the tranny wont be used. But if you put a 1g tranny in a 2g there are no mounts for the roll stoppers.
The 1g (certain years) has stronger 3rd/4th gear set, while the 2g has better synchros. Its a trade off. I kept blowing up 3rd gear, so I had to give up the good synchros and take the stronger gear set. So 1g vs 2g tranny depends on your needs. Slick shifting vs torque capacity. My last tranny was a combination of the best parts from all years mixed together.