You should find a LOT of info by doing a search on Great Planes CAP in these forums. I would recommend an engine no smaller than the OS.70. I think the new Saito .82 would be fantastic as sell as the Saito .91. I have almost unlimited vertical power with my OS.70, a little more umph would be nice. I am at 1870 feet elevation. I built mine without any real modification other than to cut out some formers in the fuel tank area to be able to raise the tank to the mid-level of my carburator. I have found the stock landing gear mount to be strong enough but my field is well groomed grass. I did change the LG attachment to just 1/4x20 nylon bolts. They broke once when I had a dead stick......no damage because I was landing fast and the wheel pants cleared the wing without piercing.

Some info on mine is here:
http://www.rcuniverse.com/forum/Need...1735946/tm.htm