YOUR FINE!!!!! The things that are going to kill a motor in a boosted application is Detonation, ring gap, AFR. Sounds like you have detonation handled with your CR, timing and the fuel you are running. Same with your ring gap since you said you run it pretty hard for 20 - 40 minutes at a time. Keep an eye on your AFR and I would say your good to go. Do you know what your temps are under the blower? I know in a blow through application an engine gets a huge advantage from the cooling effect of the air going through the carbs and the atomization of the fuel but not sure what your temps would look like in a draw through application with that 6-71 seeing how the atomization happens before the blower. BUT an intercooler will always help Blow through or Draw though. Hope this helps.