I did a little deeper dive in GMPartswiki to see if I could find something more current. I found
GM# 3997956 as a front wheel stud, 9/16-18 x 2-1/8" that was used on 1971-90 something 3/4 and 1 ton trucks/van/RVs with front disc brakes. I couldn't locate a serration size for the GM part, but a
Dorman 610-181-1 lists as a replacement 9/16-18 x 1-7/8" wheel stud for those vehicles. It does lists a serration size of 0.623".
Either way, if you are wanting to upgrade to the 9/16-18 studs it will require reboring the hub stud holes like you said as they are significantly larger than the original 1/2" studs. Does your disc brake rotor slip over the existing studs onto the hub? If so, those may require reboring too.
