Believe it or not, there is a big difference between the engine mounting beams on a .60 (and smaller) and the .61 (and bigger)
A .60 engine conforms to the standard used by almost all engines in the .45 to .60 size.
The Trex 600N uses this format.
I have successfully used OS .50 & .55, YS 56 & YS 60 in my 600N with no modifications to the airframe or engine.
The .61 engines conform to the standard used by almost all .61 to 1.20 engines.
The Raptor 60 and the X-Cell 60 use the .61 (and bigger) standard.
I used an OS 61 in my Raptor 60, and then stretched it to a Raptor 90 (using OS 91HZ-PSS, YS 91SR-3DS) with no changes to the engine mount or drive train.
On my Trex 700N, I used the YS 91SR-3DS and the YS 120SR-X with no changes to the engine mount or drive train.
You could physically mount any engine in the .61 class (OS 61, OS 70 or any 91 size) in the X-Cell 60.
The 91 size may be too much power for the older airframe.
You can fit a motor bigger than .60 in the Trex 600 - but they will be modifications needed to the motor and airframe (search "Big Block Conversion" )
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