Welcome to the club greasy. Sounds like a good project. As for your tranny, i would reccomend either a rebuild if you plan to keep it mild or a t-400 swap if you plan to apply some real power.

Oh, and joker, the 400 and 403 are quite different motors. The 400 is a small bore BB and the 403 is a large bore small block. No, make that a HUGE bore small block. It probably wouldnt be so bad with the 400 due to the longer stroke.