I had a SSE ARF with a Super Tigre .45 mounted int he stock position. It ran very well; no problems at all. I wouldn't hesitate to mount it just like the instructions show.

I also put the same engine mounted sideways in a kit built SSE. Maybe I built the kit lighter, maybe it was the streamlining from the cowl or maybe it was the carb position but this SSE was noticeably faster using the same prop and fuel. It also had a Macs muffler on this plane, maybe that was a factor too.

One problem both SSE's had is prop clearance with the stock gear. I was running 11" props. With the .55-AX you'll likely be running a 12". This means even less clearance. Order some taller, stronger gear from tntlandinggear.com or someplace similar. You'll be glad you did.