Hoping I can get some direction.
I recently got a 70 Mach1 with a 351c 4v 4brl. the previous owner swapped the 3spd manual for a T5-5spd. In the purchase he gave me the 3spd. I was under it the other day and the T5 is obviously shorter that the 3spd and there is about 1-1.25 inches of the shaft not in the transmission. Not sure if I should go back to the 3spd, get a period correct 4spd put in of leave the T% and look at getting a longer drive shaft.

Not sure if the transmission I was...

figuring out if I have the original 3spd