2 BBl Dual Exhaust

I just recently acquired a 1975 Dodge Dart Swinger with a fairly fresh 318 anc 904. It is a 2 bbl car with a 3.21 geared 8 1/4 rear. The car has single exhaust with one cat, as its a California car. The car is fairly peppy as is, but just looking for a little more. I think I am going to keep it a two popper cruiser for now. Would removing the cat and intalling a 2 1/4 inch dual exhaust make a significant difference on this two barrel car? Do I need to keep the cat, even though its smog exempt?

If I have to keep it, can I add another one and still go with dual exhaust and get improved performance?