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I think the number should have some letters in it for a VIN number on the frame. The number should be on the passenger side on frame about where the passenger sits. That number could be the part number for the frame/chassis. If I am off, others on here are more knowledgeable.Take a look at the November 13, 2016 post, it might clarify the information for you.http://forum.73-87chevytrucks.com/smforum/index.php?topic=34003.msg289406#msg289406
numbers could be on top of the framerail anywhere (even under the bracket), bottom or side... If there is an 8 digit number that would be the rail part number. They were most likely on that rail that has been sanded on.With that said, you potentially have 1979-1980 SWB frame assuming the 10bolt came factory on it.
Post a pic of the inner/outer pads, I'll check 'em out through the MSI book. Part numbers on the shocks might narrow it down, but probably not much.