They also make carbed intakes for Vortec heads. The Vortec heads with the right cam, and Edelbrock air gap intake WILL put down 400 horsepower on a stock 350 bottom end. Considering your bottom end isnt worn out. I have personally had one with stock bottom, STOCK vortec heads and springs, Edelbrock intake, and cam(dont remember specs but you dont need alot of cam with these heads) 750 Holley carb that put down 377 @ the tires.
Do a google search for Vortec head swap.