if you are going to buy the engine new i would look hard at a zdz40 or 60, or maybe some of the sachs type gas engines.

do you know how much weight you will need up front to balance it? the zdz will be relatively light compared to a zenoah 45.

have you run the st yet? i would break it in and then evaluate the engine- my super tigers need at least an hour to start to run well at the low end and then you can start to really tune the mid range. but then you may already be experienced running st engines so this may be nothing new.

ed