New ^ lug front brake rotor Wheel combo question

[chevykevy]

I recently purchased a set of 6 lug disc brake rotors for my 68 chevy short box project. When the 6 lug wheel is placed on the rotor, the inner diameter is larger then the diameter of the rotor. The rotor maintains the inner diameter that a five lug rotor would have but the 6 lug wheels inner diameter is larger. The wheel will not center itself so I must carefully tighten the lugs so the camfer on the lugs center each individual stud. Is there a spacer available? Is the fact that the wheel does not center itself before tightening the lugs a problem? Aftermarket wheels don't rely on centering either , do they? Any comments to give me piece of mind would be greatly appreciated. Thanks

71 GMC long stepside, 56,000 original
70 GMC 3/4 ton fleetside
68 Chevy project(The Wheel Question truck )