Anyone use fuel system cleaners?

Just wondering if anyone uses fuel system treatment for their A-bodies. The new-to-me '70 Dart i got in September still has the fuel in it from the previous owner. I've been driving it here and there but haven't filled it yet trying to get rid of the old gas; Its getting a new fuel filter today, so thought Id ask if there's any recommended products to help clean up any varnish/ old crap. I've used STP fuel system cleaner and Castrol Techron products in the past on my newer cars. Anyone have any thoughts or will I ruin stuff using those products?

Any thoughts are appreciated!