Unless that machine is worth the bucks your best bet is to just fine a parts machine with a v twin. I'm fairly certain the flywheel from the higher hp motors will work, at best you swap the stator as well.
I had a Vanguard 16 that needed a ring gear and couldn't find the parts, they wanted $500 for the kit then. I went to the junk yard and took one off a larger vanguard and it worked fine. The balance and ring gear were all fine. The yard made me buy the whole engine, but for $40 it was better than the cost of a new flywheel. I miss that junk yard, the epa forced them out of business about 5 years ago.
I had a Vanguard 16 that needed a ring gear and couldn't find the parts, they wanted $500 for the kit then. I went to the junk yard and took one off a larger vanguard and it worked fine. The balance and ring gear were all fine. The yard made me buy the whole engine, but for $40 it was better than the cost of a new flywheel. I miss that junk yard, the epa forced them out of business about 5 years ago.