The Fly in the ointment (we say that up here
) may be the diameter of the shaft vs guide hole in the block etc?? But you can always machine the hole in the gear larger or possibly make a sleeve for the shaft?
Or better yet, remove a section of the 351 shaft, reweld it. Then grind or true it in a lathe and use a 302 housing and size bushing(s) accordingly.
Here are helpfull hints on actually getting the installed length correct.
http://www.fordracingparts.com/downl...tM-12390-A.pdf