I'd look more into getting your squish velocity in order as you bump up that compression. Also(for optimal results), as you increase compression, your exhaust ports may need to be increased in size(wider Is better if possible). The KX250 jug has an exhaust that works great for high comp already. The increase in size is due to the more efficient burn, producing more gases and pressure. More pressure=more port area to breath.
I've started researching the math for this today. I'm going to look into how optimized the 1st gen tecate is for pump gas and if anything else can be squeezed out of it before going to race gas. Casting aluminum is on my list of things to accomplish... Of course, so is owning a CNC lol.
As for clearance, there is a few rules of thumb out there for piston to head. Don't quote me on this, but it may be something like 1mm-1.3mm for 250cc set ups. <- I'd go research squish velocity and squish clearance.
I just wanna go fast. If your not first, your last!!
Reproducing the Tecate CDI. Contact me if you need one. I'm most accessible on FaceBook. You can find me on the 1984-1987 Kawasaki Tecate KXT250 Group.