I've got yokes in two lengths, the driveshaft in my 77 Comet was also too short to suit me. They yoke was only engaging about an inch of spline in the transmission tail. I swapped to a longer yoke I had from something else, I don't recall what it came from though.
im in the same place that you were, mines only in about an inch but i don't know what has a longer yoke that i could use??
If you get the long yoke be sure that the splines actually engage further. Some of the long yokes have the same length splines and the front of the yoke is just there for transmissions that have the tailshaft bearing in the case farther. (63 galaxy with the "Cast Iron" Cruis-o-matic used these)
