NEVER stack your HG's that would be the dumbest thing you could ever do, plain and simple. If you want lower compression get a Cometic HG, remember the thicker the gasket, the more prone it will be to leak/blow. You could get that setup saftly down to,10:8:1 I would run. Run at least 93octane and a conservitave timing map and you will be ok to run around 6-10PSI, you could push more but that all dependes on the EMS system you end up going with, and how good your tuner is. Dont try to run a hack or a FMU and expect the motor to last long with that kind of compression.. Best of luck with whatever you do