I've converted several old Tamiya KT using the HL gear boxes. I've used the standard ones (tiger box as the output shaft is long enough. You will need a strip of 2mm sprue to separate (space) the gear box from the side of the tank (it also keeps the gear axels from rubbing on the side. I use millioput to set the motors in place then when hardened I use small screws on the side and bottom to secure the motors. It has worked perfectly. You will need to grind flat one side of the output shaft to fit the tamiya drive sprocket (easy with a dremel) I just got the 3-1 gear box from RC Command and will install them shortly. I've been usuing the stock gear box with the white capped motor with a 8t pinion. It's worked fine (especially I have metal tracks) but the 3-1 will make it a real stump puller. You can also use the HL turret travere ring and motor (but you will have to space the ring to fit (I use a strip of sprue - don;t recall the thickness) I usually buy a cheap 1/24 HL tank off ebay to get all my miscellaneous parts like turrel ring, turrel motor.gun elevation motor etc /upper wire harness. you will still need the smoke and sound electronics. Its easier to do than you think