Chances are it has multiple keyways. With your compression issues you might consider retarding the cam if it is currently advanced 4 degrees. This will shorten the effective stroke and lower cylinder pressures a bit. Do you have the specs for the cam? I.e. advertised intake and exhaust duration and the lobe separation angle? Assuming 270/270-110, if you install it with zero advance the effective stroke drops to 2.441" vs 2.523" when it's advanced 4 degrees. Using the earlier example this would take your dynamic compression ratio from 8.4:1 to 8.16:1, which is not insignificant. If you have the cam specs we can get more precise about the effects.