I think Erson can provide them also. There are only a few, very few, places that supply cores and they all get them from the same place. You may find that a smaller shop will be more receptive to one offs because that is how they produce all their cams. No CNC cams from Erson. Contact Steve Tanzi stanzi@pbm-erson.com
The following was given for the Chevy 4 cylinders but should be the same for the 6s.
Jalopy45 says "If you run a roller cam you use chevy SBC lifters and Olds 350-455 tie bars..>>
Push rod guide plates you use the 350-455 Olds or the 151 chevy for the 1977-79 engine."
Beater