Your head looks fine, the only thing different I do is blending the radius around the valves I do not sink it into the ceiling so it will not cause turbulence when the valve is opening and the air flows over the valves, other than that if you are allowing more the correct side clearance to the valves and increasing it as it opens then there is absolutely nothing wrong with it. I'd buy it! This is more personal preference than anything but I do not trust copper gaskets on the Kohler motors, I always use the old black stuff Vogel use to push, but if it is working for you then don't change it!! I would not spend a lot of time and money on your fuel issue, get one with enough octane so it does not pre-ignite but has good fuel weight around 0.750" specific then stay with it and don't mess with it. I used C-16 from VP fuels when I ran the gas class but it is really expensive but if you have something that you are comfortable with use it and move on to other issues. You might try adjusting the timing from 26-30 if you can hook more than once on the same track to try and give yourself some comparison if you do not have access to a dyno, make sure you have the appropriate plug for the fuel you are running. I couldn't even try to remember which one I used on gas just get the correct heat range. Your problem seems to me something small bacause to me it is right in there where it shoud be its just getting the fine edge and thats when you start looking at basics, or little things because you have the big ticket issues handled.