Should I do a Cat delete on '75 Duster

Typical. Didn't even bother to read the details of the post and you don't know anything about California smog laws. The OP's car is exempt because of its age. His car never has to be smogged, or even inspected, ever again. As long as the title remains clear there's no reason anyone with any official capacity has to look at that car in person ever again in California.

That's why I bought it! It'll make engine swaps and the likes way easier, and getting smogged is such a hassle here