Well I have Just finished building My rv4 and have mounted a OS .61 fx that I had for my P-51 onto it. It seemed CG wise that It was going to be nose heavy but I moved my 3 servos back one bulk head and it feels perfect. It just needs a couple of more stripes and it will be airborn this weekend. I still havn't put the cowl on cause I couldn't quite afford the fiderglass cowl. But when I can it will go on. It looks great and I have a good feelin about it. It will be my 4th plane and my second build. I started with a superstar 40 trainer until I had a mid air with one of my friends extra300, then I bought a GP P-51 60-90 and it hasn't left the ground cause its so heavy and I couldn't afford another powerplant yet. I have a SIG p-51 that I have flone.