Thanks for the comments and suggestions. Another machine shop, recommended to me, quoted $2500 for a rebuilt 400, 4-bolt.
I don't think, that with what I'm looking for in a motor, I'm going to go wrong with the 350 crate. Thanks, Ghetto Jet, for the link.
Astroracer, thanks for the link, too. I have thought about this off and on and now would be the time. This probably is the best answer to the mpg. issue.