I can go measure the bolt locations on my 1951 bed. They'd be relative to the front and sides of the bed.
Give me a few minutes. Is your GMC a short bed 1/2 ton? [on edit] 78" long woulbe be a short bed.

Front bolts are 1-3/4" behind the front panel and 6-5/8" inside the bed side (measured above the angle strip)
Rear bolts are 53-3/4" and 73-5/8" behind the front panel and both 2-7/8" inside the bed side.

Last edited by klhansen; 08/25/2024 8:48 PM. Reason: added dimensions
Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.