It does seem a bit much to me. I am thinking that they mean 90-120 4 stroke?? OS doesn't make a 70 2 stroke that I know of, so do you mean an OS 70 four stroke?? If that be the case, I think a 70 would be too small. A 70 is usually used in place of a 46 2 stroke for a 5-6 lb. plane and the AT6 that you refer to would require a 90 2 stroke due to the weight. [8D]