It's been many years but I seem to recall that someone in the midwest area (OH, MI) was doing Model A engine rebuilds on an exchange basis. Any ideas if that still happens? Like I said it's been a long time.
Try Ron's Machine Shop in Shandon, OH (Near Cinci.). He is always set up at the Hoosier Swap & Show. His phone is 512-738-7353 oe email BKRL@aol.com. Ther's another guy from somewhere in IL but I can't lay my hands on his card. You might throw this question out on The Fordbarn's Model A forum.
If you're looking for somewhere in Illinois, these guys are recommended... http://antiqueenginerebuilding.com/
John Wolf in Ely, Iowa usually has a stack of rebuilt A engine longblocks ready to go. Call his cell at 319-361-3424.