The small Honda 2hp outboard is air cooled.
Other for thought:
Also I have seen another way to go from vertical to horizontal drive with a v-belt and pulley half twisting. A 7 hp lawn mower engine vertical was geared down before or after the belt not sure which, then it drove the rear wheels of an art car wagon.
I pulled from the trash a motor like this and low and behold the self propelled front wheel drive with gearing down box was driven by a half twist belt drive right above the spinning blade on the shaft. Holding in on the pull handle tightened the slack in the belt to act as a safety clutch to stop the mower if it got away.
Looking at some of how many of these other than motor bikes are built can give good ideas to use on the motor bikes.
I though found it easier, or at least thinking I'm saving in cost by getting fixer-uppers at the flea markets for side shaft engines. I think it was 15 dollars and got two Briggs side shaft engines and knew that I had enough spare parts to get them running. I bought new gaskets and cut both the valve and seat angles by taking them to a machine shop $40. The compression so much better on both engines.
A junk yard for bike parts or whole used bikes I found at Faber’s Cyclery in San Jose, CA. Just opened on Saturday is what I hear. Best to call and find out.
Faber's Cyclery - San Jose, CA
Handle bars I picked up there were really good without the chrome gone and cost way less than new. A lot of rusty stuff as it sits outside, but just as long as it is only on the surface, many people on this site paint old sytle frames.
Measure Twice