More basegaskets will lower compression from stock, not good for rpm but the engine will run cooler. Changing the port timing without at least changing the shape of your exhaust shouldn't increase rpm but it will change the powerband of the cylinder, shifting peak power lower or higher up the rpm scale depending on what you do with the port windows. However, matching the case transfers with the cylinder transfers if not already done will increase rpm by ramming more premix into the combustion space. High-compression cylinder heads will raise rpm. Something new I've been reading up on says that the position of the sparkplug in the cylinder affects combustion efficiency. Some have the plug straight through the head (E50) while others are offset (Sachs 5 series). Will read more