I need a little advice from some of the more experienced members here. I would like to know a few rules of thumb regarding the right size planes to put these conversions in. I like flying over-powered and I am convinced that the gas / glow conversions are the way to go due to the weight reduction and elimination of the large rotating mass associated with the flywheel.

My first conversion will be a Ryobi 31cc. Is this too big for 120 sizes sport planes (Yak, Extra, Giles) ?
My next conversion will be a Poulan 38cc. I'm thinking maybe a 80" UltraStick might be a good choice.

Are there any guidelines you use (ie wing area, wing loading, etc...)?
Most manufacturers recommend engine ranges in both 2 and 4 cycle displacements. Do you apply some conversion factor to determine applicability of these gas / glow conversions?

Thanks for your comments and suggestions