My recommendation...buy these parts and bolt them on:
http://www.rc-monster.com/proddetail...od=rcmcenmount
http://www.rc-monster.com/proddetail...MFPbatterytray
The motor mount will put the motor on the same side as the servo. Then you mount the battery tray on the other side of the vehicle. These parts take away all the guesswork of trying to do a homebrew conversion...especialy the motor mount.