Your cheapest, simplest way to go with that is an adapter and the big 2bbl Holley used on 360, 383 and 400's. It's 500 CFM, simple as dirt and bulletproof. If you can't find a suitable 4bbl, hit me up and I'll set you up with one.
I will vouch for Tony. I have purchased a few things from him and he knows some things about the slant as well. Including the carb he speaks of for my slant.