I can't answer that question.
I have set up two trucks with 350/TH400 and was able two move the crossmember back 4 inches to secure the rear of the transmission while retaining a level engine.
I do not know how low you plan on having your engine/transmission, nor how lowering the rear of the truck will affect pinion angle.
You are going to have to figure out the rear transmission mount as you go along with the build.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission