ok with your open chamber heads i would say if you don't polish the combustion chambers them i would say 10:1 - 10.5:1 compression.

some people have luck alot higher 10.5:1 it all depends on combustion chamber efficiency, quench, timing, piston top shape, if the engine runs hot or cold, how much overlap your cam has, and so on.

it also helps if you buy aluminum heads.

p.s. go to a double roller timing chain insted of gear drive because the crankshaft sends harmonics to the valve train (not good), they've even been known to pop keepers out of the retainers(also not good). plus they take more horsepower, and they make a noise you like at first but you take a trip in the vehicle and you want to kill yourself when you are finished IMHO.

Randy