Another option to consider: Edelbrock makes an intake makifold and a camshaft to fit this engine. Don't know how much horsepower it would produce though. I've see them in summit racing equipment's catalog, or go look at
http://www.summitracing.com
I bet this setup along with a 4bbl and headers would produce a nice extra bit of horsepower. But the 20 thousand dollar question, exactly how much Hp??