MM,
I know of one friend that used the 25 and said it was just like the 35. For the Ringmaster I would run the mounts past the lead edge of the wing about 1", put lighting holes in from the back of the engine to the end of the mounts and use 1/32" plywood back about 1" past the end of the new mounts, add some 3/4oz fiberglass/epoxy reinforcement around the wing fuse joint. I did this to mine and have used the Fox 35, PAW 15 diesel, OS 20FP, OS MAX 25. The ship is over 20 years old and not cracks or loosening of the fuse wing joint.

Best,   DennisT