[Bicycle Bob]

I'll second the notion of starting with a 4-cyl crank and cam to make a two-banger. I'd only do it if I was going to do some serious streamlining to reduce the power needed on the highway. A 3-cyl with an extra-mild cam and tall gears would probably be my preference for reduced power, though.
I used to prefer even numbers of cylinders except on radials, but now I realize that the inline 3 only stops one piston at a time, while fours stop all four at once.