Dave wrote:...

"Is there a reason you have not listed the GM series for
consideration."

The only GM series engine still being manufactured is the 9.8 HP
1GM10. The 'Y' series has (apparently) superceded (sp) the GM series,
due - I suspect - to stricter environmental regulations. Since I need
20 HP (per the plans I'm working from), the new 3Y20 seems the only
logical Yanmar choice.

MW