It's the tranny locator bore that is different. Nearly all of the SBC and I-6 Chevy bellhousings have either a 4-1/4" or 4-11/16" center bore. The SM465 needs a 5-1/8" center bore.
Replying to this slightly old thread, just in case you didn't find a solution, I think this adapter plate would work for you.
http://vintagemetalworks.blogspot.com/p/s10-t-5-to-gm-5-18-diameter-bore-bell.html
