I spent some time looking at engines for mine and the YS 1.10 was just perfect. It didn't need any lead or move the servos around to wierd places. Even the fuel tank sits over the CG.

Now YS has a 1.15, The 1.40 is a low rpm engine and it's hard to get high pitched prop for the 1.40. I would think you would need something like a 15x15 or something in that range.