Advice needed

I think everyone is trying to be nice in explaining the same thing - those heads and that cam are never going to make 500HP.

If you consider it takes 400 HP in a 3500lb car (no driver) with "sensible" gears to make a flat 12, (give or take 20HP) you can see how much off the boil the current combo is.

I recommend you set yourself a HP target and aim for it....plenty of knowedgable folks on here can steer you in required head flow, carbs and cams once thats settled on.