There are two ways, that should help, combine them, and you should be able to figure it out.
1. The flywheels probably have a heavy part (point on perimeter) to them. Put the engines at TDC, and see it you can fit the heavy part of the flywheel opposite TDC. Usually the heavy part is an external balancing of the engine, to counter the reciprocating mass (piston and rod). If the solid/heavy part is just a counter to a heavy stell insert, and the flywheel is neatrally balanced, then obviously that won't work.
2. The flywheels will have a magnet or a piece of steel/iron in them, to induce current when passing the magneto. See if either fits so that that happens when piston approaches or reaches TDC.
If both tests above come really close with either flywheel, I don't know what to do.
DKjens