driveshaft help

i am working on a 91 seirra it had a 4.3 in it the peopled that own it let someone talk them into putting a 350 in it then decideed for gas and other reasons to put a 4.3 back in it. now i can not get the drive shaft to go in the back of the tranny far enough to seal and not stip out the first time they dive it i am lacking about 1 inch or so and the carrier bearin on the crossmember for the drive shaft has been moved back about 1 inch so can anyone help me please. this truck has not run for over a year thanks kagan:banghead: