Larry
Crane cams is the supplier who currently grinds the GM factory replacement camshafts for GM. Most of the guys here who are running the 143 cam are using the Crane unit, which is an exact blueprint of the GM cam.
Unless you're dead-set on having a cam that comes out of a GM cam tube, you can buy the
535 blueprint cam from JEGS. It's identical to an original GM cam.
Eric