RE: Electrifying a great planes extra300 .46 size
I did an elecric conversion on a World Models Rambler 45 a few years ago and used the E-flight Power 46, 5S 3700 battery and APC 13 x 8 E prop. It pulled around 1300 watts and gave great performance.
As far as notor mounts go, you can buy a commercial mount or mount the X-mount to the fiewall using long bolts passing through nylon stand-offs (from Ace Hardware). Tower sells aluminum mounts if you prefer that route.
Rob