Since making original reply a need arose to replace a badly damaged
water jacket on a single arose. No water jacket for a single was available from my usual source. Adapting a more common upper water jacket from a twin was only option. Turns out to be pretty easy,
Interesting enough to turn into an article for Antique Outboarder.
The water jacket for single and upper water jacket for a twin are
the same EXCEPT for extension on single jacket to match up with
water tube. All that is required is a disk of right thickness to
file, fit and try. The disc was drilled and parted off from a short
bar of aluminum in junk box. That part best done with lathe, but,
could be done with drill and saw. The rest was file and fit.
Only upper water jacket wit work as it has the arms to mount tank.