Were the perches you remove the ones from a torque tube? They won't work. They have that rubber bushing in them and will flex real bad if welded to an open drive rear end.
If your 3 speed auto has a final drive ratio of 1 to 1 (no overdrive), you may want to look for a 3.08 rear end for better highway RPM.
Carl

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