Sounds like your heads are winners - I would still encourage a port match.

I concur with Rrumbler as to the 400 being a good motor with a lot of pull and as long as the steam holes are correct, they last as long as any SBC. Once they've overheated, there can be some real problems with cylinders and head warping. For a while, they were plentiful in wrecking yards, but not so much anymore..

The TH-400 is a great base for a bulletproof three speed.

Have Fun,
Glenn