Unfortunately there is no reason to build a small V twin. All the manufacturers, B&S, Kohler, and the like all start at about 16 HP, and they are pretty big, I have one. I am going to strip it down to the basic block and see how big it is. I was thinking that if I cut off the crank on the flywheel side, close and made a flywheel up on the drive side with an integral sprocket, I wonder how narrow I cold get it. I saw small home made V twin, it was done with two Honda S90's would work perfect but it looked like a lot of work. Have fun Dave
PS: Another Idea was to use a V twin Compressor block and build some heads!