RE: Which Engine?
The truth is, just about any glow or Diesel model engine that runs reliably and has a displacement between .32 and .91 C.I.D. will fly the CGM Cub reliably and well. It simply depends upon the flight performance that you are seeking as to how much engine you need on the nose. I have flown CGM Cubs with .40 thru .91 four-strokes and with .40 thru .61 ABC two-strokes. If you have ever owned a hot .32 two-stroke, you know that they will swing an 11x4 prop with ease, which will easily fly a CGM Cub.
Now, if you really want to have some fun, install an OS or Sanye (ASP/Magnum/SC) .32 glow engine. Fit said .32 glow engine with a Davis Diesel Development conversion head and fly a day's worth of flights on a single 16 ounce tank. You take your model, your R/C transmitter and maybe a spare prop to the field and nothing else for an entire day's worth of flying. How's that for compact? Tell Bob that Ed sent you.
Ed Cregger