[dcb]

I agree that piston removal and leaving the valves closed is the most efficient approach. I bet you could take an air cooled vw and delete the front left and right rear pistons and pushrods pretty easily. Might need to cut off the big ends of the con rods and use them as a spacer. The odd fire isn't a huge deal, many of my bikes (including my current one) have uneven firing spacing, big whup.

Or custom grind a cam and turn the 4 cylinder into a two cylinder with two cylinders of "boost", or a 1 cylinder with three cylinders of boost and have the deactivated cylinders pump air/fuel in to the remaining cylinder.