i got a 4ac I'm my ae71 thats been rebuilt with port/polish, bigger valves, mild cam and electronic ignition and i can safely say it could take on a tired bigport! It revs to 8k and i can slide 2nd gear with a locker so don't discount the old 4ac for performance potential. If i had the time, i would make up an adjustable cam gear so i could shave the head a bit more and bump up compression... but make sure you run it on 98 RON at least.
or
if you don't give a crap about the engine and its life, get an oxy bottle, and run a line to the top of your air filter hat... :dance: