Interesting possibility of using some motorcycle parts. Just checked out a few motorcycle starters in the age and cc range. They had a different flywheel end. It was splined instead of a gear that sprang out. The brush heads were different also. But there may be a possibility that some cycle armatures and stators are the same. I'll give it a shot and take the parts to a Yamaha dealer and see if they can match a cross.
The machine has a pull start so no problem. The YS828 is up and functional though and a tiger with full compression. I'm looking forward to trying it out against a 828 and 11/32 Hondas if we ever get any snow.
It would be nice to get a starter though to get it complete. Below is a YS624TEN with a starter. Nice enclosure.
BTW: the 624 and 824 are rated at 6 and 8hp @ 4000. Sort of weird for 202cc and 291cc engines in comparison to Briggs and Tecumseh ratings at 3500. You'd think the Briggs and Tecumseh might be more capable but just the oppposite is true.