I have a literal box full of pot metal / plastic short-shaft gearboxes, tracks not full sets but I order really cheap plastic parts from TankArmy.
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Tiger I - Panzer II - Panzer III - Panzer IV - Chi Nu Kai - Panther G - KV-1b 756(r)
M4A3(76) Sherman - T-34/85 - M3 Grant - SECRET PROJECT