A lot of the '50s Ford products had overdrives that were the same length as the standards.  They would interchange without driveshaft modification.  I put a T85 with OD in my '56 Bird that originally came with a standard light duty trans.  I just had to change the yoke on the driveshaft to make it fit.  No frame or tunnel clearance issues.  Birds were available with overdrives when they were new.

John

The T 85 will fit T birds with no problem and the shifter will work.  But there was something a little weird about the early Birds which may go back to the 55's also. It seems to have been a running change because the OD's used in the 239 256 and 272 pass cars were not holding up.  So Ford started buying them from BW even before BW had cast the tailshaft housing to match the standard Ford setup.  Hence you can see in the '56 shop manual a T 85 with a heavy plate mount that bolts to the tailshaft housing rather than the cast mount.  None of this makes a dime's worth of difference unless your buddy wants an exactly correct '56.  Then it was probably a running change that ties into his car's serial number. If this interests him he should contact Gil Baumgartner (SP?) of CTCI who knows this stuff cold.