I usually always replace the engine hardware provided in ARFs. I did in fact use the motor mount, as much as I did not want to (I simply did not have anything else that fit!). As some had previously mentioned, my engine mount holes were pre-drilled but did not match up with the mount holes. I simply added another 1/4" ply plate to the back of the existing firewall and redrilled, adding 8-32 nults/bolts. I mounted an OS 46fx and this does great! I'm sure an OS50sx would do a bit better. I also use a Zinger 12x5 prop and hovers are stable and the engine is responsive when needed. It does pull out but not with great authority (not too good for beginners). And YES, I do use separate aileron extensions (I don't see how you can get away from this without installing a Y-harness inside the wing). As you guessed, this is for harrier and other programming. You don't need flaps for slowing down,... actually, sometimes you need to drive the darn thing to the ground.