IMHO, no on the GP 42. TT Pro 46, OS 46 FX, and OS46 AX, Yes to all of them. The GP 42 will not have enough thrust to easily fly this plane. If it gets it off the ground it will be a struggle to keep it in the air. I first tried an OS 40 FX in mine and it wasn't enough for this airframe with as much drag as it has. My Elder is "scaled out" with flying wires, a machine gun, etc., flying off a grass runway and I found a 46 FX to be much better both for takeoff roll and once in the air. Others claim to fly theirs with an OS 40 or 46 LA with success. I am not an advocate for overpowering everything you fly but the GP 42 would have it's work cut out for itself in this "brick". If you do want to try the 42 have an up size engine that will bolt right in using the same mounting holes, throttle linkage, same weight, etc. ready and waiting for an engine swap. My 40 and 46 FX were a direct bolt in swap so it was easy and I planed for the possibility of swapping them.