ORIGINAL: mrbigg
I have seen one of these with a DL 50 and it gets up and runs. If both engines are going to cost the same, I'd go with the one with more power. I've seen one fly with a G62 and it landed the same as the one with the DL, so the extra weight isn't going to be a problem. Pe, what kind of props/rpms are you getting? Does it run good with a standard cowl/pitts muffler?
The engine runs well with all kinds of mufflers. You tune the carb and get what you choose for.
With a restrictive in cowl muffler, the 22x10x3 prop is an excellent choice, and will pull a 25 lbs plane about straight up.
In response to flyfast:
If the Mustang is not tail heavy, The MVVS 45cc engine with mag case is the ticket I think. It has the torque to pull scale props like 24x8 and even 24x10 or 22x8x3, but also will run well up in the 7000+ range using a 22x8 or 20x10x3