Topic: engine
The 1GM10 seems to be the engine of choice for repowering the Contessa. Why do you want a 2 cylinder?
My boat has a Yanmar 2GM13 (fitted with a Campbell Sailor prop) that has more than enough power. It's smooth and quiet, but not a major difference when compared to the 1GM10. The 2GM20 will probably be too tight a fit to be practical.
Unfortunately, there are few used engines around here. When they get tired, they're rebuilt. The 1GM10 will cost approx $5500 USD.