That is true, Eugene, for the Tiger 1. With him, you have to bore out the wheels where the stock bushing goes. On the Kings, both versions, the bearings are a simple installation, just drop them in. I have instructions on how to do that for the Kings. Pz 4, I don't have one yet, so I don't know.
When boring the plastic wheels on the Tiger 1, you have to be very very accurate in the bore process. A little off centre and you will either destroy the wheel or have a wheel that wobbles, in other words it will be off centre.
Will you be coming to the Meet at Kubinka this summer? Lean'chka and I will be there. Alexei from Mockba is doing the coordination for it. Do you know him? If not, I can put you in contact with him.