A 4.56 gear seems a little much for that cam. But that car is very heavy so it may be OK. I think a 4.11 would be a little better for a street car.
Isn't a gear vender a 28% OD? That would make a 4.56 to a 3.28. Or maybe it is a 22% and then your calculation with be correct. not sure.
Yes, your heads are the weak link to making power. Bowl smoothing is the low hanging fruit when it comes to head porting. Pull out the valves and smooth out the transition where the bottom of the valve seat meets the port.