With a 4 stroke there are two ways to raise the compression. You can either skim the crankcase to lower the barrel or you can make a longer conrod. Personally I'd rather skim the crankcase because if you overdo it then you can add shims . The one thing you really have to know accurately is how much clearance you've got inside to play with. This could be the piston to head clearance and the closest approach of the valves to the piston around TDC. Although I've never owned or played with a 4 stroke I can see where the problems are, especially with a Saito which I believe has an integral head/barrel.

The guy I mentioned in post #17 did his experimenting with Saitos (I think mainly an 80) and I seem to recall him saying he machined about 1mm off the crankcase but that was to use zero nitro.