Hello Henry,
If you look a few lines down in this section on a ChangFa thread started by number21 you will see a lot of discussion by him, Mobile Bob, rcavictim and others about 18-2200 engines. Be sure to find the Yanmar web site listed and open up their agriculture single cylinder engines.
For your space problem take a look at
www.Utterpower.com  PGM  experimental (ChangFa) engine set up. Looks good and compact. If interested you'll want to get on the waiting list.
Member TheSitRep is posting good results with this PGM gen head on this forum. Look up his posts.
Also if you look back on oliver90owners posts, he states quite clearly what most us believe . . . there room enough here for many engine types.
But I think for duribility/longevity you reaaly what to turn the speed expcetations down from 3600 to 1800. Besides, if you look at my engine listing I can tell you from experience that after about 2 hours of 3600 RPM you'll be dizzly numb or so wound up you will be ready to kill something.
Reguards
SteveU.
