Paint Question and Tag location?

[513100]

Hi, I am the new owner of my first old truck. Its a 51" Chevy 3100 216. A couple of questions right off the bat,
- The color is blue and looks very old, hard to tell if its original. The cab and door jams are not painted blue, but rather a brownish red? Just wondering if this is how they were painted.
-Second question is where can I find the location of the paint or body tag? I can't find it anywhere.
- Last the 216 has a knock at all temps, It doesn't sound like its coming from the lower end. Any suggestions on where to start?
Thanks for any and all help in advance!