Taigen KV-1 lower hull uses 48mm shaft and Taigen 3 to 1 gearboxes will fit but the tank will be too fast. I have heard that the Taigen 4 to 1 gearboxes will fit but you will have to modify the exhaust system to get the upper hull to fully seat. I used Taigen low profile brass gearboxes in mine but they are no longer available.