I use a gasket for a '90 KX250. The head gasket is thinner, boosting compression. It is not a huge difference in power, but it did give mine a little more snap. When you rebuild the engine, you can use a Weisco piston for a '90 KX also, part# PS-90.
You asked if it would ping MORE? Does your bike ping now? I have never experienced pinging with my bike, even though it is far from stock. If your bike is pinging, you have a jetting or timing problem, or you are using gas with too low octane.