Did you read this article: http://www.hotrod.com/articles/dyno-tested-make-700-hp-trick-flows-new-fe-heads/

We used a XR292R-10 street roller in it. It is roughly the same size of engine that you are talking about (482 vs. 496) and similar compression ratio (11.37 vs. 11)

The XR292 works great in an engine this size. It is big enough to make plenty of power but small enough that the idle should be half way decent. It won't idle like a Caddy, but it should have decent vacuum and be driveable if you have 3.23 or 3.54 gears.