Not so much difficult as different. Methanol burning engines are, relative to gasoline engines, quite the fuel guzzlers. For small engines it's not that big of a deal but once you get into bigger engines you are flowing a significantly greater amount of fuel. I dont remember the exact amount off the top of my head but you need like 50% more methanol than gasoline for efficient combustion. What that means for you is that you will have to close the needle quite a lot more to run on gasoline. If your carb has o-rings they will also need to be gasoline compatible. Since the SG series of pumps are gasoline compatible that part of things should work and substitute for the built in pump in the Walbro type carb.