Generator replacement

I have a Generac in my 96 Dolphin. It works pretty well the only thing I've replaced is the controller. The generator is noisy, leaks oil, and the exhaust is very unpleasant. My previous motorhomes had Onan 'Quiet' series generators that were trouble free and could not be heard in the coach. I kept several manuals on my old Onans and I took measurement around the existing Generac. Seems really close dimensionally. Has anyone installed an Onan 5.5KW 'Quiet' series in their Dolphin. Thanks,
Mike Layton