ORIGINAL: heavyaslead

Your only option is to upgrade gearbox and motors separately, Markus Horn out of Germany produces a very exspensive rock-solid ball-bearing raced gearbox for the Tamiya tanks for around 300USD.

As for using 540's, the Leo power plant is the only feasible option as a drop-in (use that term loosely) for a serious upgrade to the WWII tanks whether Tamiya or Hen Long!