To answer your actual question, it will bolt right onto the bellhousing. You will have to figure out the shift linkage and get the right yoke-to-driveshaft connection, but it bolts right up. The disadvantage to a T-5 is that you have to modify the input shaft.
You might not like the 1st gear ratio of the M20, though. It may be a bit sluggish for a six depending on the gear ratio of the rearend.
With a 3.07 rearend and a 235 or 261 you want about a 2.5:1, which matches the original 2nd gear of the 4 speed with a 4.11 ratio. This puts you into 3-groove Saginaw land, but if you don't mind a bit of clutch feathering the M20 should work just fine.
