I've been going to my local mechanic shop for years with my 2 other cars. They don't try and find things wrong just so they can get work. They look at issues I have questions about, and don't charge and don't "find" problems if there aren't any. I trust them completely and believe what they say. They talked me out of buying a Ford PowerStroke, too many issues. They run a good, honest business. Hard to find these days.
So I showed all the photos of the underside of the truck to the shop mechanic, the diesel mechanic (he said his first preference would be a 12-valve 5.9L Cummins), and their father the owner of the shop. They all looked it over, zoomed in on the photos.
They all said the same thing: "That's not that bad. Pretty normal for a Pennsylvania vehicle. I would have expected worse."
I asked about what looked like a crack from rust in the radius arm mount. They said, "It's surface rust and the crack is not a crack but a seam between the two halves of the mount" (it's true, I found a photo of an unrusted mount, it also has the same seam).
I asked, "If I get this truck then should we replace any rusted parts?"
They said "No, leave it alone. You don't need to spend money doing that."
I repeated at least 5 times, "Guys, if you tell me not to get this truck and keep looking, I'll do exactly that. I'm not committed to buying this truck. The price is good, the mileage is really low, it drives well and the body and interior are perfect. But if you tell me to pass and move on, I have no hesitation doing that. I bring my cars here, and I'll be bringing this truck here. YOU GUYS ARE BUYING INTO THIS WITH ME. IS ANYTHING, ANYTHING YOU SEE A DEAL-BREAKER?"
I tried hard -- I really tried many times -- to get them to tell me to pass on it. I went into their shop looking for them to confirm that despite the truck is beautiful, the rust is bad and I should pass on the truck.
The mechanics and the father who owns the shop all said, "I wouldn't pass on it. If you like it and it drives well, then get it. It's fine. I recommend that you get it."
I know it doesn't look good underneath, but I trust my mechanics. I appreciate everyone's advice to seek the trusted advice of my mechanic shop -- their answer wasn't what I was expecting. Thanks again, all!