What is the 84 T5 out of and going into? Make sure the input shafts are the same diameter where they enter the crankshaft. I have heard that 5.0 and 2.3l T5's are different diameters. Its is not "TOO" hard to swap an input shaft if you have experience with trannies.
4 cyl trannies have a tiny input shaft at .59 i think while v6 and v8s have .688. there are a lot of info at turbford on t-5 specs so you read it yourself.