Center boring a GM transport wheel

[stewmagoo73]

I have a small dilemma. I have a 67 c10 typical 6 lug drum brake set up. I recently acquired a complete set and they just will not fit the hub. The center hub on drum in a conical shape and it doesn't like much to fit flush.

I thought about a spacer kit and bought one but it just doesn't fit flush over the lugs either.

Does anyone know what diameter I need to have my wheels bored to?

Thanks in advance