OM606 with an SD350 pump is the way to go. Simple. far too much power, but gentle with it. I think an OM650 with an OM 662 pump would be better, but brutal on the clutch
Mike, Rory is back in December, he has a need for some special fibreglass boaty tech, as he's now looking at racing Seagulls. I'm sure he would be happy to take a look (see re-build) your other lump. Alternatively, he can sort the cam on my old lump, you take that on (everything else has been re-built and it has the stage 2 head on) and you leave one of your here, for me/rory to re-build to give to Youngie as a return for letting me have my replacement engine...
Is that complicated?