383 rebuild - kinda whimpy on the dyno?

If you pop off the heads goback with a steel shim head gasket to help comp. I've seen stock heads make over 400 hp with not much more cam in a 383 and peek at 6000 rpm. I read an article once that showed big valves without porting actually hurt flow on the 906 heads. That should be a 360 to 375 hp build imo.