Hasn't Ernie got a four cylinder Yamaha running with a gearbox? I think he fly's it every other day for rotor test flying.
We have a three cylinder Yamaha engine here ( NZ ) that's been waiting a while for a gearbox. At last we have the time ( if not the money ) to finish this project. This is a gear drive bolted directly to the engine, not some sort of adaption.
Like our EA and EJ series gearboxes they look as part of the engine. These will not be " project managed " to be sold before we are happy with long term tests.
I saw Ernie's Blue Tandem Dominator at Mentone. It appeared to me that he had replaced the Yamaha 4, 150 HP EFI, with a Viking 100-110 HP EFI, which uses their Viking gear box on the end of it. Unless he now has two blue tandems, I don't think he has the Yamaha 4 mounted on a gyro anymore. He did seem pretty much fed up with it last time we talked about it, as he never got the electrical system sorted out on the EFI and engine would suddenly quit and go to idle forno apparent reason every now and then in flight.
(I went a slightly different route, using carbs heated both electrically and engine coolant (liquid). I am really happy with it, and the engine simply won't quit if you have an electrical problem. You can lose the ECU, the regulator, even the battery, and it will continue to fly just fine - unlike any other conversion EFI engine in use today, including Yamaha, Soobie, Honda, Viking, whatever.)
I called Ernie up, seems like he is really only interested in those Florida-built Vikings...that already have a gearbox mounted up to it.
BTW: The output shaft end of the YG3 crankcase is blank. There is no place to fabricate, alter, nor install an adapter or a gearbox. I take it you are using the magneto end of the engine to bolt up one of your PSRUs?
You should contact me with price and availability of your PSRU, as right now I have two other customers who may be interested in your unit perhaps in place of the Canadien one I have been selling with the conversion kits to date. Send me a PM, I'll give you my phone number and email if you don't have it handy.