Genuine GX200 Project

Hello everyone. I have not posted here in quite some time, but I am looking to get my bikes going again, and this Gx200 is on my list of priorities. This engine will be limited to being run on pump gas only. I am also trying to stick with stock size valves for now. I do not want to buy parts that I will replace later, because I cant leave anything well enough alone. In its current state it is;
No governer
Stock block, head, cam
Flat top piston
Billet Rod and Flywheel
GX390 Carb
3 Stage, long header

I knew most of this information at one time, but just like anything else, it slips away from you eventually. I want to raise the compression ratio, but I am unsure on which head is better to start with. I understand the the 14cc and 18cc heads are bolt on's, but would the 22cc head flow better after milled?

What is the limiting factor for lift on a stock valve head build like this? I was looking at Isky's cams and the Black Mamba cam looks to be a good match for what I am trying to accomplish (.275" LIFT 246 DURATION @ .050" 108 L.S.A.). With .275 lift and the 26 lb. springs, would coil bind be an issue? Typically at what valve lift does interference start happening(flat top piston and .080 milled gx200 head)? Would a higher ratio rocker arm be acceptable with this cam?

Thank you for any and all input, I am sure I forgot a few things. I will add them as they come up.
If you already have the gx200 head mill it .08-.09, ratio rockers work great with the BM cam, you might have to go heavier springs with 1.3 rockers if you go past 7000rpms with that combo.
You should not have any interference with what you have listed.
Stock valves will support 15hp no problem.

The gx200 head milled is a great flowing head... With some light porting...round off all the sharp edges... You should have a nice kick with the parts you listed...

What rod did you put in it? If you went with the .02 longer rod you should be about .02-.015 in the hole. With the flat top.