RE: AlleyCat & 60LX
The alley cat is a phyically larger airplane. Really needs an 11" or 12" prop to perform well. Some fly it with OS91 or YS110 power.
The 60LX is a heck of an engine, but it is better suited for the "40" size airframes. 60LX prefers 9x7, 9x8 props, and 10x6 is as large as you want to go.
You are taking a good approach with the idea of trading weight, but in this case the 90LX is the way to go.
Bob