Buck-O-nine,
Sell the 4-speed to some one who's restoring a '68 Camaro, for a reasonable profit, and either go with the T-5 or a four speed that matches your bell housing pattern.
There are no bell-housing swaps for the stovebolt six, except perhaps to the pre-'47 bell housing, which is not helpful.
You'd have to change to a later engine (post '62) to have bell housing "swappability".
There is a Dodge truck 4-speed from the '70's that has OD as 4th gear, and is supposedly a direct bolt-in; it's usually found in 2wd trucks w/ slant-sixes.
Good luck.
