I have had 3 drive shafts shortened for different cars. the older car drive shafts can not be shortened. they are double wrapped, meaning there is an inner shaft, a layer of vibration dampening rubber and then another tube on the outside. the easiest thing to do is get a drive shaft from a 70's/80`s truck or van and have it shortened. although they are larger in diameter, they are not double wrapped and can be shortened.

*sorry I just reread that you are swapping trans. in a truck