If the bolt and dowel pin spacing of the flywheel is the same as the engine, just drill out the flywheel to fit the larger bolts. The dowel pins carry the driving torque, so you can make the holes a few thousandths larger than the bolts if necessary. The later model engine uses a 7/16-20 bolt. That's only a slight enlargement of the existing hole, so the 7/16" drill should self-center in the existing holes if you use a drill press and align the bit carefully before you drill each hole. I'd suggest using a 3/8" bit to align with the hole, clamp the flywheel to the drill press table and then swap to a 7/16" bit to enlarge the hole.
Jerry
