drive shaft flanges are different i believe.do you have the 78 shaft, if so you can just use the lower half of the 78 shaft.i just used one of the round flanges from a 60 drilled new holes,
the only reason that you fron would be turning at a different speed than your rear is,different gear ratios,sounds like one of the third members was changed out a one time, one probably has 3,73 one 4,11, check the gear ratio in the rear first,its most likely the one that was changed. mine was...