IMHO an O.S. 46 LA would be "just right" in that CG Eagle 63. The 46 LA is the exact same size and weight as the 40 LA (or 40 FP) yet makes 20% more power. That's the one you want if you are flying off grass. Either one will fly the plane fine once in the air but the 46 will do a much better job getting it up to flying speed thru the grass on takeoff. There are lots of them new or used on Ebay, and Tower still sells them new at about $85. I too am a fan of the O.S. FP and LA series of engines, you just have make a good engine to airframe match. They are easy to start and tune, reliable, and are "fuel sippers".