here is a Nextar with a OS 61fx,I used that engine because it was a spare I had,and I wanted some extra power for float flying otherwise I would have left the 46 in there,that plane had a through overhaul,rebuild, and recover job done on it.
the ARF plane is set up and drilled for the iso-smooth engine mount so if you want another engine with a different foot print your going to have to get a new engine mount as well as redrilling the mount holes in the plane if it doesn't line up correctly.
the mount provided is metal and is set up to use rubber engine mounting bushings so there is not actual bolt holes in the engine mount either,it also doesn't have any room for play,it took a little work to fit the larger engine in the space provided, I also had to cut the fuse to make room for the larger engine as well,I didn't really care because it was stripped of covering but somthing to consider when chosing to mod or deviate from the recomended parts the plane was designed for