I'd steer clear of the metal gears (sorry rob, but I can't let you off-load your crap if it will cause grief to somebody else!

) My T34's (x3 operational battle tanks with 2 more in the workshop) run fine with the plastic gears, if you want 'better' then put some asiatam gearboxes in (major surgery warning!)- those aftermarket metal gears will wear out the mounts far faster than the stock ones...
Take out the battery box with Doctor Dremel , tape it shut, swap out the electronics for HL - I prefer the RX-14P over the -18 personally - and fit a DBC. The chassis is light enough not to need the metal gears, the drive doesn't get tangled in grass like the Pershing or Bulldog, and the tracks are broad enough to keep the long stuff at bay anyway.
HTH
Mart