A '71 455HO has "round port" heads. Large chamber, though.
We recently built one ('71 455HO) for a man in Mass. He dynoed it just Monday (chassis, '69 GTO). Heads were ported to 250 CFM @ .600 (int). Comp solid roller 236/242 @ .050, .620 lift. Torker II, AED 850HO, Super Comps.
With 93 octane, it made 407 RWHP and 435 RWTQ. That "converts" to about 480-500 GBHP and 540 or so lb. ft.
I doubt you're making more than 400 -420 HP with that Edelbrock cam ("generi-grind"). But you ARE probably making 500 lb. ft.
Dave took his car to the track a couple weeks back (same car). It went 12.32 @ 111 (best ET) and 12.45 @ 114 (best MPH). 60' times were in the toilet, as he had "street" tires (1.9-2.0). 3,810 lbs. with him in it (weighed on the track scales). With good traction, easily an 11 second car.