ED

funny thing is that i went through exactly the same dilemma as yourself!
i bought a os91 FS II because they are on sale here in Aus and i have wanted one for a while... i also bought an excelleron 50 ARF. Some people thought it was way too much motor for the plane, but it is a biggish plane with a fairly thick wing. The instructions on the box state up to a 80 4 stroke; well the 91 is bugger all difference! I considered an OS70 surpass II, but the 91 was only about 2mm wider in the crankcase and 7mm taller...

As it is, the rocker cover only pokes through the cowl by a smidgen...
I cant believe that a 40 2 stroke would have been enough to fly the plane..
As it is, i havent finished construction yet, but i am sure that it will be "agile".

One thing i did, was to add some reinforcement to the engine bearers.. i epoxied in some hard triangle stock where ever i could and also in the tank area... then i glassed inside the tank area to add more strength.

I am hoping the rubber isolation mounts will help take some of the vibration out of it too!

The other members on this site that have the excelleron 90, believe the 91 4stroke, is way too small to power the plane..

let me know what you end up doing....

mike