Although all the engines mentioned are good... I think the .50 will be too much for your Airplane...
I am pretty new to R/C Airplanes but I have still to work out why people go with OS engines when you compare price...
You can buy a SuperTigre GS-45 ABC engine from Tower for $69.95 or the .51 for $79.95 and you are going to go with an OS costing $159.95...
Flag and buy the SuperTigre...
Matt