1) Well, the center of the crossmember has to come out, no if ands or buts. And this piece has load from the torsion bars on it. So your guess is good as mine but if you don't have enough the center of the floor pan will pull in/down from the load of the front springs.
2) The 42RH is a refined version of the A-500 with several improvements and upgrades over the original. I'll try to scan in the information from my instructors manual today and post. It was the last "904" based transmission that still had a hydraulic governor which is why I selected it.