Heres a NOS set of Vortec heads, 906 stamping. They have never been on an engine. Excellent price, but shipping might be steep. Don't let the Ebay listing scare you. These guys are in North Carolina, and sell mostly new and used race stuff. I've bought from them, and they are legit.
Compression is an easy way to gain power...torque AND horsepower. Your currently pretty mild on the compression side. Raise it up to say 10 or 10.5:1. Keep the intake runners on the smallish side, talk to an engine builder that understands camshaft theory, not just sells camshafts. Talk is usually free, so no harm there. Tune your stuff. I can't say enough about tuning your carb and ignition to work in harmony with each other.
http://www.ebay.com/itm/NEW-Pair-SB-...item5422f49c74