I am in the middle of building one, using the Wilesco D49 engine. It's a twin V, and almost too wide for the boat. If I were doing it again, I'd go for an in-line two cylinder engine, or an oscillating one cylinder. The disadvantage to a single cylinder engine is that it won't reverse.

And the shape of the hull makes it a bit difficult to get much speed - but then the original didn't have much either!

What ever engine you choose, make sure that it is firmly fastened down. These engines shake a bit, and mine almost came adrift at one point.