wrote:

Not a stupid question at all. In fact it has been done to the air-
cooled VW head and isn't all that hard. Far less work than making a
casting. IMHO water cooled aircraft engines have some real
advantages.

BUT..............

There are lots of individuals that prefer the simplicity and
reliability of an air-cooled noise maker.
===========================
Leon McAtee

If this is that simple, perhaps it's worth doing. There is a small
electric water pump used in Mercedes-Benz heaters that could be used
with a motorcycle aluminum radiator that just might to the job... It's
worth thinking about anyway.

Many sport bike radiators can be had used cheap off eBay because they're
so well tucked in that they don't get smashed when the bikes crash. I
recently bought a Kawasaki 500 radiator for $12...

Tony