I'm getting a "bouncing" thing on acceleration and deceleration in the drivetrain sometimes. (stock 79 12a) is this possibly a bad motor mount?

 

Could be a bad motor mount or anything else that leads to free movement in the drivetrain. My car does it on decel sometimes because of how much slop is in my differential, but I'd start with checking the motor mounts like you mentioned. These cars do tend to buck a little naturally, though, depending on what's done to them.