wrob: If I'm correct on the engine mounts being the same as all the other ARC planes ( and I'm pretty sure I am ), it shouldn't be much to remount the engine. The biggest problem I forsee would be having to cut the crap out of the cowl. If I did it I'd side mount the engine.

As a bit of added info on these planes: if you are carefull you can use a heat gun to reform some of the plastic. I suggest a heat gun and a pair of gloves to do the forming and keep from burning your hands.

Also when assembling :: SCORE all glue areas, the instructions say to lightly sand but using a hobby knife and scoring gives a much better glue joint.

CBJUSS: I don't have the weights of your engine but if it is close to an OS 61 it should work fine, it might be a close fit but I've seen a couple with 91's in them. Even on a 2 cycle it is some times a bit of a job to fit an engine in but IF you take your time a little playing around will find a way.
GOOD LUCK and ENJOY !!! RED