Sweet Rob. You will not regret the decision! The Rambler is a great plane. In terms of the engine... I imagine that the Siato 72 would be a sweet engine but I have had no experience with them. I do, however, have too many O.S. and Y.S. engines :-) I would say the FZ63 would be killer. Of course any O.S. 70 would be fine (Surpass II or Ultimate). Personally, I would put in a Surpass II. If you don't want to spend that kind of money, A Magnum engine isn't that bad either. I'd had their 30 (cute but weak) and their 61 fourstrokes. They don't have the same kind of precision machining but they are good for normal duty work. Quality has been perfect and deadsticks 1 in about 50+ flights. Still don't know what happened... my friend flew her and was trying to get her to hover. Little did he realize that a 8lb+ Cessna Skylane with a 61 fourstroke isn't suppose to be able to do that kind of stuff. hehe. He overshot the runway on the deadstick and cartwheeled her in the grass. Repairable :-)

Anyway, what am I saying here? Surpass 70 or if you're a little more adventurous (or cheaper) a Magnum (ASP) 71.