I have just purchased a Beaver too, and also trying to decide on engine choice. From all the info I have read, You will need a 3 plus h.p engine too get it off the water, but the 3 cyl. would sound awesome. I am going to purchase a gas , just dont know which one.
here are my 5 top choices. Somebody help me out and set me in the right direction

ZDZ 40 rv-l
3w 28i
Brillelli 46gt
evolution 35
Zenoah 45

Which one would you use? for reliability, easy start, doesnt shake the plane apart.