Rims for KH disc brakes

I read that you believe that the issue is between the hub OD and the wheel ID. And I assume that you have cleaned them. I dont read that you have put a vernier caliper in there and measured those.
So I respectfully suggest that you remove the caliper, move it inboard some where and attempt to mount the wheel with the caliper removed thus. I know its a tight fit between the caliper bodies and the wheel structure. Its also a tight fit between the hub and the wheel.But the fit should be loose enough that you dont have to beat it on.I can seat mine with just a bit of muscle.
If it still doesnt fit you will know what to modify
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If it does fit,then I imagine there is interference between the caliper and the wheel structure. The caliper will need to be moved inboard or the rotor will need to be moved outboard.You could also remove the grease cup and see where the cotter-pin hole is relative to the castellated nut. If theres considerable room there, its fairly easy to move the rotor/hub out. Or perhaps the bearings are wrong or the inner bearing stop is factory machined too deep, or a bearing has spun in the past, and "machined" the bore too deep.
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Or the center register in the wheels are just plain too small. And that would be very odd, since they fit on the back ok. I have a feeling the hub ODs are; rusty, damaged or incorrectly machined.
All the best