that CR seems high for 91 octane if you want to be in a good quench zone with correct gaskets. I'm no expert, but don't you want to be around 9.5-9.7:1 even with aluminum heads? My motor is 10.2:1 and I run aluminum Eddy Performer RPM heads on my 451 and still detonate unless I keep the timing 32 total or less. I'm running .037 thick Cometic gaskets.