Here's one of the best ideas I've seen for this (see second post in the thread): Tech week- Model A simple tricks to update your car - THE H.A.M.B.

This assumes you've still got the Model A rear to scavenge from, and that the perches aren't all wallowed out (like they often are).

Ken's correct about drive shaft length, Model A was 103-ish inch wheelbase, the '40 112 inch, so you'll have to have both the torque tube and drive shaft shortened by a competent driveline shop or machinist.