I started with a ST 51 in mine. I also had to trim the fuse for muffler clearance. If I could give a little advice. I installed my engine last. There is a limited space for the batt&RX in this plane. So I mounted it first. Then when everything else was installed. I put the SE on the CG machine without the engine. Then I set the engine on the bottom of the mount. This way I could slide it back and forth to get the CG right. It ended up with the engine forward on the mount. It looked fine and gave me the correct CG with no lead. If I had mounted the engine in the recommended place it would have needed lead in the tail.

David