Magnum, servos??
I used Hitec HS 605 MG servos on elevator and aileron, and a small HS 81 MG for the throttle... just because I had them around.
Any standard size servo will do, if it hasn't got to much slop in the gears.
The 605's on a 5 cell baterry are pretty strong... IMO if you use weak servos you better go with real hinges instead of the CA hinges in the kit. Real hinges move more freely...