1967 C10 - Rear frame damage or rear springs?

[mr.precision]

The rear of my 1967 short bed step side sits about 2" higher on the passenger side than it does on the driver side, when measured at the wheel well. It's also quite visible when viewing the bed from the rear.
Not too many frame people around these parts, so before I go to a shop that can measure the frame my question is: do the springs wear in a different way over the 51 years this truck has been used? Or is this definitely a bent frame that will require some attention.
I don't know where to start, but it's gotta be fixed.
Thanks

[Grumpy old man]

Your floor looks pretty level climb under it with a tape measure , If it's ever been towed using the rear cross member they can bend and give that result , In today's throw away world there aren't many shops with frame machines or guy's who can run one . easier and cheaper to pull the bed and really get a good look at it, could be something simple ?

[bill3rail]

Check bed mounts.

[chewychevy67]

My truck does this exact lean too. Before I powdercoated it I had my frame checked and it was square. I also put all springs and suspension in new. Interested in what others say. I figure almost all old gm trucks are this way

[ohboy321]

I recently put new EZ Ride rear springs in my stepside, and after letting them settle for a bit my bed was tilted about 1 -1/2 inches to the left when measured at the fender well. It was tilted before the new springs went in, but I wanted to wait until after they were in to make any adjustments. Measuring from the concrete floor I found that the frame was only off by about 1/4 inch by the rear bed mount. I ended up making some shims to level the bed out. After that I was able to line up the side exit dual exhaust and the rear bumper with the bed. It looks pretty good now.