The key here is to get a motor in the 230-240KV range so that on 10 cells a 18x12 or 19X10 can be used. If a smaller prop is required you can either up the KV or the cell count. The Dualsky 6355DA motor series come in a few KV options that should cover just about any combination required to do the conversion.

Xmotor DA series version 4, XM6355DA