The RCV website engine info suggests a two blade prop of 13x6, 14x6, 14x7 sizes. so a 13x8 three blade is a reasonable choice then.
Master airscrew happens to make a 13x8 three blade. http://www3.towerhobbies.com/cgi-bin...XAA39&P=ML
The RCV engine does not have poppet valves so overreving it is not a big issue, you just wind up outside of its power band then.
http://www.rcvengines.com/rcv91cd.htm