On my ARF I mounted a OS91 Surpass by making sure I had enough room for the fuel and muffler pressure lines and in front of the cheeks like 'The_Matrix" said. However, if I had it to do over again, I would have moved it further forward. I ended up putting a lot of weight on the nose. Also, not sure if you will experience this problem or not, but watch the cheeks when your engine is running. Mine had a lot of vibration and the left fuse cheek began to pull apart from the side of the fuse on the bottom. I fixed this problem by taking a dowel and running across in front of the engine and drilling holes through the fuse sides and into the dowel. Then I screwed in a couple of Cowl screws with washers. No other problems with the vibration since then.