Yep, that probably explains it! As annoying as it is, your best option assuming better fuel doesnt work is to either swap to the engines original fuel injection in, complete with the knock sensor/sensors or swap to throttle bodies and a new ECU (megasquirt, emerald, etc etc) along with a knock sensor or two if originally fitted to selectively avoid the pinking.
Bonus of the second route is that you will get a much more driveable and powerfull engine,,,,,,,,,,, at a cost whilst you may still get problems if running stock injection and igition, without mapping to suit if possible. Other cheaper alternatives are to fit a programmable ignition system (relatively cheap compared to the full throttle body route but still needs mapping and may result in some nasty flat spots) or possibly to fit some really wild cams (and make it undrivable on carbs!) or lastly to fit a stock head with a light skim though you sound like you want the oomph lol and the head may have been breathed on a bit in other places if the CR is pretty high.
