Most Yanmar dealers also stock the Aluminum Universal Injection elbows. Then you can build a 'dry stack'.
With such you can get a QM Yanmar threaded exhaust outlet flange, and use common 'black iron' 1-1/2" threaded pipe, 2 90° elbows, Add automotive muffler cement to all the threads to 'seal' ... add the injection elbow, cover all with insulation 'lagging', run a new water hose from the exhaust manifold directly to the injection elbow.
This dry-stack configuration will also create a 'siphon break' between the engine and the wet exhaust.
The Downside of a 'dry-stack' is that you will have a LOT of heat in the engine space - consider to keep the blower on when using the engine.