I am not sure what a sm465 is but here is my 2 cents worth. I have a 40 Chevy with a 302 and used a mid 50s Chevy truck bell housing along with the truck cross member and rear motor mounts. I have used both a 4 speed Saganaw and a T5 on the Chevy truck bell housing and both their shaft lengths fit right into the pilot bearing just fine. I don't know if you can easily switch to a Chevy truck bell housing on your project, but it worked for me. If I remember right, the Chevy bell housing is about 1/2 inch shallower than the GMC.
