I would change the cam and degree it so it is advance 3 to 5 degrees on the intake side and try that before lowering the compression ratio I ran 10.78 to 1 comp. ratio on my Duster motor with the last set of heads(76 CC Indy SR) on the motor before I sold the car, it ran great( 9.96 at 134.7 MPH at 3450 Lbs through the muffs) on 91 octane Oregon non ethanol pump swill I had a set of 84 CC Eddy RPM heads on it also, they had 10.29 to 1 compression, the car ran low tens with them on it on pump gas That motor had no signs of detontation ever on either set up What spark plug and heat range are you running now and how much total timing are you running ? I think your location is at or close to sea level, correct?