I have a Great Planes 40 size Mustang. It has an old 70 OS surpass in it. Its mounted inverted and runs great in this application. The model balanced with the battery behing the wing in oil cooler scope and needed 1/2 oz of lead in the tail. Now I have OS,Saito and YS engines. They all run good. How much lead would it have taken if I used an .82 Saito? Its much lighter than my 70. I agree get the plane first then pick an engine for it.