Catalytic Converter

Modern cats are not at all like the early parts. On anything truly streetable (not "streetable" if you get my drift) I doubt that you would notice a difference. I've done the "Test Pipe" thing, no difference. Growing up in the 60's -> 80's I have seen the difference that they make in clean air. You do want to breathe clean air I'll assume. Once I get it's AFR under better control I'll be putting a universal cat on my '65 Valiant. Check out what Summit, Jeg's, etc. sells.