I also bought a set supposedly modded for a GMC. The only mod I could find on them was where they ground a flat spot and stamped GMC.

Here's how I adapted mine.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.