I know people are going to jump all over me for this but IMHO if you don't put a 4 - stroke in this bird leave it in the box. I had a GP SW for 3 years with an OS 120 in it and it was one of my favourite planes. The 120 was ideal power and weight ( anything lighter will require nose ballast ) and the best part of flying it was the 4 - stroke sound. I had many flyers comment " it just wouldn't be the same plane with a 2 - stroke" and no it wouldn't be. The ST75 will fly it just fine but your going to miss out on 1/2 the fun.