I would suggest a bigger 4 stroke than the 56 that you are mentioning, maybe the new .81 will be a good choice as it has a close displacement as an OS 46 AX.
http://www3.towerhobbies.com/cgi-bin...?&I=LXSZW5&P=0
You will want to look for Hitec ball bearing servos which will work flawlessly and can hold the punishment of the 3D flying:
http://www3.towerhobbies.com/cgi-bin...?&I=LXDEM1&P=0