Check out the The Goodwrench Quest articles in CHP. They took the 290 HP Goodwrench engine and started bolting on add-ons. Part IV they bolt on a set of Vortec heads. They claim they got up to 371 HP on stock heads with a 750cfm carb and a little tweaking of other things in the setup. Take the numbers as you will. Read the whole set of articles. They're interesting reading. I'm sure someone else here will chime in with the validity of their numbers...

http://chevyhiperformance.com/techar...64/index3.html

http://chevyhiperformance.com/techarticles/46364/