Probably the most you will get for the least work is gov. removal, but I doubt that the intake or exhaust, even if modified, will be able to breathe well enough to spin it much faster than the governored speed. The most work for some power would be to take the head of and mill it down (there are a lot of different calculations that must go into this for all to go well). Of course this would require higher octance fuel, 110+. As a free air motor, they are very limited in cooling capacity, so any increase in compression (more heat) will definately shorten engine life considerably. I wouldn't worry about any higher octane fuel if you just gut the exhaust or do other simple mods. Higher octance can actually cause lower performance in low compression engines. Lots of guys used to try to do this on sleds, and it has been proven to be ineffective. 85 will be fine in most cases.
