Hi Dave.
The Edelbrock performer RPM package with your carb will make a real 325-340 bhp ish on an engine dyno. I went down the route of importing AFR 165 heads on the back of various US based mustang magazines that showed collosal horsepower from the AFR's. After further upgrading to a 331 stroker package i only achieved 348 bhp on Tim adams engine dyno . Tim really knows his stuff (he builds the engines for genuine 40's cars in the masters series and le mans classic).
The engine had perfect mixture and ignition but showed only a 20bhp gain. I was using the Holley 600, comp cams 280 magnum Roller cam / pertronix electronic ignition and 10:1 forged KB pistons with the 331 crank and rods. Seeing all these dyno plots showing over 400bhp is very surprising and Tim does have a strong view on some of the claims made . He has dynoed hundreds over the years and reckons 350bhp from a 10:1 engine with a fast road cam and a 600cfm carb is pretty good going.