I have put a 51 rear under a 40 one ton GMC. I think you need to check the master parts book (can be found online) to double check, but I think the TT will need to be shortened. The other issue can be spline count on the input shaft versus the transmission. That can be easily overcome by using 2 u-joints and making them into one with two differnet spline counts on a given end.
To further help, is this truck short or long bed? What is your transmission?
