There is a big difference between the older 3 way cats G bodies use and modern ones. Our older cats require oxygen to be pumped it from the smog pump while modern cats generate their own oxygen. Stock MCSS cats are already high flow units. The big issue is that G bodies are legally limited to single cat, split exhausts, true duals are illegal due to never being offed from thd factory that way.
80's honeycomb cats are not restrictive like 70's pellet cats are. As I said, MCSS use wide mouth, short cats for even less restriction. I would not call 9 or 9.5 CR low compression either. Stock exhaust manifolds and cheap mufflers are bigger restrictions than the cats are.
All aftermarket cats do not clean as well as OEM, nor last as long. On the Ford Panther forums, they warn not to use aftermarket cats as they blow out every 30k like clockwork, that is with OBD2 EFI and DBW. Its a major problem with ueing headers on a Panther as OEM cats won't fit.
If you really want to be fast and dirty, buy a new modern car, and rip the emissions out. You would be good for 7 years as they don't inspect new cars until then. By the time its 7 years old, it will be outdated and slow compared to the even newer cars so you will likely want to upgrade again by then anyway.