in most cases heli engine have a shorter crankcase and a differant muffler and a bigger head fins. For the shaft you may have have to put the engine mount on shims, as for the muffler that can be changed easily if it's in the way, So chek the muffler, if it cost prohibitve to change the muffler it may not be such a hot deal, but if youe like me and have 3-4 spares sitting around its probably a great deal. I've put plenty of buggy motors on planes and those are pretty close to heli engines.