(I pass this on for a friend from Holland. Pierre)
We own the Rasmus number 647 in the Netherlands. Our ship has a Volvo Penta 4 cylinder MD22L from 1995. Besides standaard volvo penta minor details (rusty impellor house, which is leaking very often) we are very happy with the engine. Is has something like 55 Kw power, which is very good for a Rasmus. Especially in rough weather at sea, such an engine, in combination with a double reef sail gives a lot of happy people on board. Because the engine room is not very isolated from the rest of the ship, I would advice you an engine with a low rpm. Low as possible. This saves you a lot of noise during motoring. Some people in our harbor are very happy with mitsubishi engines. Perhaps also an alternative.
Good luck with your engine project and of course with your great Rasmus. We have ours since 6 years, so we didn't repower by our self, but we are very happy with it!
If you need any other info from us, let me know!