Probably the same as most any factory 8-lug wheel. I have been buying wheels for my K/20s for decades and all anyone every needed to know is width and diameter. This stuiff comes from back before things got weird with wheels and tires.
Cali, really dig your truck. Looks great with the vintage narrow beauty rings. I had to put the dark grey F250/350 wheels with 255/85s of my '95 Suburban for a while, when a 35/12.50-16.5 on 9/75 slots went kaboowee! The 285s on 7" are a nice look for these trucks, even with 4" lift. Here is my '72 w/4" lift and 255/85s on 7" Accurides.
And on the 'burb