By far the biggest limiting factor of the FE motor is cylinder head design. A few companies have figured out how to make them work - Edelbrock is one. If you need to stick to iron heads for authentic looks, you need to have bigger valves as well as porting to make them flow almost as well as a
stock big-block Chevy.
It gets expensive real quick to modify iron heads. Modern aluminum aftermarket heads are much more bang for the buck. Maybe paint the aluminum heads or something.