Cometic Gaskets, can cut you a copper head gasket in several thicknesses. I think they can go up to 0.080".
I just dont like them though, never had good luck with them on a water cooler engine. Now an old air cooled engine, dont want to use anything else.
205 compressions not that bad, you could probably get by with a 50/50 race/pump mix, maybe less than that.
Do you understand the benifits of race gas. You dont have just any ol 4 wheel atv, man thats a TRX250R, best sport quad ever built & sold & needs to be treated as such.
Neil