If I could figure out how to accomplish this, I'd build me up a twin based on Echo cylinders/pistons rods.
Anyone got any ideas?
In the 70's I owned a Yamaha motorcycle dealership and we rebuilt cranks for singles an twins. At that time a twin crank was simply two single crank assemblies splined together. The two inside flywheels were splined and a light press fit. A Lambreth seal (also used in steam turbines) was used to prevent cross flow between cylinders. The case was split horizontally. In the 70's individual crank parts could be purchased. The inside spline would be the difficult part to machine.
A trip to the motorcycle shop might produce many ideas.
Bill