I think 81 had the 305 too, no? doesn't really matter as i think john you said the engine has been replaced.
If there are no sniffer requirements or any equipment required, and you don't care, you can take it all off. I can't imagine most emissions reducing equipment to actually add performance. That doesn't mean take out something like an EFI system just because it reduces emissions.
You can take off all the equipment, get rid of the cats.
Bob is correct about the semi-computer controlled 81. Many people i have talked to complain it creates problems for service and such, but you may not have that problem if the whole engine was changed. in 82 there was corssfire which AFAIK was throttle body injection. As i understand it the fuel is injected somewhere in the intake, instead of in the individual cylinders.
Take off the equipment, open the exhaust up, you can also try to change the thermostat.
I think that higher temps or compressions can yield more efficiency and potentially power but also produce emissions.
while you're at it add some lead.
My point is if you really have no regard for emissions you can just reverse alot of the changes in the past 40 years
tom