On this VK Nieuport I use a .56 saito with a recessed firewall glued to the rear of the forward Cabain struts. I mounted the engine inverted and put the servo for the throttle as well as the battery forward of the firewall. The .56 is overkill but I am swinging a 13x5 wood prop and when these photos were taken I only had to use a brass spinner weight to get the CG in specs. She jumps off the ground with plenty of rudder control and climbs like a rocket. Most of the flight is at 1/2 throttle. I was worried about the 4 cycle running inverted but have never had a problem with the Saito cutting out. I use 15% nitro with a OS F type plug. I just set it up for a good idle on the bench and then mounted it inverted. No problems since then.