I did exactly what your talking about.
I bought a new T5z, removed the tail housing, and sourced a S10 pick up housing with a mechanical speedo drive, shifter and the top cover. .See the photo for the difference. All this swapping around takes only minutes. However,,,because the speedo cable hole is now in a new place, the drive gear does not align with the new hole. We ended up replacing the output shaft with a Chevy T5 unit and used the S10 drive and were golden. There are people who say you can shim the driven gear in place on the Ford shaft but I chose not to do this. We also installed .83 5th gear at that time
The rear drive yoke will have to fit the Chevy splines also.
This might help explain better
http://www.flatheadv8.org/t5-swap.htm