I've had some time to start doing some measurements it definitely appears the frame is off in the rear by about 1" on the right rail (too high). Width wise in the rear, it's swayed inwards by about 3/4" (by going off the factory measurements I found in the service manual).
Standing behind the truck, you can definitely see it has the gangster lean going on the left side of the truck. Measuring from the bottom of the wheel opening on each side also confirms the same height difference as the frame.
Although the VIN tag on the truck cab and the title match as a genuine short wide, the number on the driver front frame rail is "7Z18558" doesn't match the last 5 digits of the VIN. I've also found that the rear frame rails have rather jagged edges on the rear and some plates welded on at some point. Does this look like a long bed frame that has been cut down at some point? Does anyone have any comparison photos I could compare mine too?
Given how much hacked up stuff I'm finding in the rear, I'm seriously considering putting on the No Limit raised rear rail kit and re-doing the bed floor. If the frame is not the original one, I won't feel so bad about cutting it up. I don't know where else to look to see if the numbers match. I plan to take the bed off over the next week or 2 and look closer.
Here's some shots of the rear rails:
And here's the PO's lowering kit (the blocks are 1"), but I can't find a brand on any of the parts.
Here you can really see how bad it's leaning to the left:
