Possible frame is twisted??

[Mattys1970C-10]

So I was looking at the suspension yesterday and now im gettin kinda worried that its not a backyard lowering job, but that its a twisted frame on this truck I just bought. somebody told me that the right rear corner of the truck sat higher than the left, I said it was parked on a hill but my OCD (plus the fear of spending 4500 bucks on a twisted truck) drove me to check. I dont know how to verify if the springs were heated to lower the truck, and they did one side a little differnt than the other, because it sits like a 4.5 6, or how to verify the frame is all good. are there points I can measure? Things to look for? Sellers to hunt for?? any help is greatly appreciated