Following. I need to do my tailpan and posts, but not looking forward to it.
Started the passenger side.
Observation:
1. These were constructed using humans on a line. The spot welds are totally random. The passenger side has 5 or 6 additional spot welds and all in different locations. Guessing you get more spot welds if the welder had a fight with the wife the night before and fewer if the welder was behind on his quota of completed quarter panels.

10-4 Copy that
Is this related to rear quarter panels, or are these the front inner wheel wells (i.e. new thread)? What you're showing doesn't look too terrible. I would sandblast that, coat it and re-use, versus waiting to get questionable aftermarket parts...Doing a rust repair on my 76K5. Assessing how to approach replacing inner wheels wells now. I got so much rust, that many of the attachment points from part to part are hard to evaluate. All the bolts that attach the wheel wheel housing to the inner wheel wells came out fine. First question I have for the K5 folks. The original inner wheel wells are stamped as part of the inner bed walls on my 76. Each bolt location has a "weldable" bolt. Does anyone have advice on weldable nuts, or other way to bolt the inner wells to the well housings?
Also, I also have been waiting for LMC to restock the driver side inner post tail backing plate for months and months. Looked on the website tonight, and for the first time it was "in stock" Yea ha. ordering ASAP
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Related to replacing the tail pan and posts. Before I removed the rear tail gate, I was aware that the vertical gaps between tailgates and posts were not consistent when the tailgate was up and locked. The gaps were wider at the top, than the bottom. The previous owner had to add fender washer shims under the upper tailgate lock to compensate for what appeared to be a spreading out of the tops of tail posts over the years to get the tailgate to lockup properly (see pictures). I always thought that there was a sagging problem with the severe rust of the tail pan and tail posts. The rebuild would be the opportunity correct what I thought was a sagging issue from rust. Today I measured the box at 4 points, and discovered that the main rails were nice and parallel, front to back (dim A & B). But the tops of the post were 3/8" wider than the bottoms (dim C & D). This explains the gaps I saw with the tailgate installed and locked in the up position. I would appreciate it if others could measure their box rails at the points you see in my attached photo. Would greatly help me in figuring out if and how I should correct my K5. Cheers!
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Yes sir I do that’s why I’m replacing Tall pan and all floor pans front and back because rust is my issueIf I'm reading your measurement correct, it looks like about 66 1/4" at the top. I can't tell if the other end of the ruler is anchored to the inside post edge, but if it is, you have a bigger top-to-bottom spread than I'm dealing with.