do something up top, not below
Scott is correct here, just add a layer of headgasket ( that is if your using a mono head design), if you use a extra base gasket it will do the following, it will reduce the compression alot more, because it adds to your overall deck clearance, now just instead of raising the head area, your adding the entire piston top and deck height to the equation(more volume). Plus, your going to advance your port timing by raising this up, this is what is referred to as the "poor man port job", with a viper I wouldnt do it as they are already respectable, and if you have trail ported cylinders, its going to be even more of a change, meaning if your exh. port is already raised from porting them and your raise it more by adding base gaskets, your going to lose even more compression and raise the powerband of the engine to a higher rpm. As for the base gaskets, the srx has the better cooling holes then the viper base gasket, the stock yamaha gaskets range from about .010"-.011", thick, if you have seperate cooling heads on this sled by all means run the srx base gasket, it will help with the cooling.