It does match the VIN. My engine code is W which is part of the VIN. The red box is mine. CK3 stands for 2 & 4WD 30 series. The part number on my emissions tag corresponds to this. It threw me off for a while after I bought the truck until I found this page and learned emissions standards changed mid-year. The code below mine is for trucks made after 1/1/85 and would have 2 smog pumps and the stainless exhaust manifolds. The Federal tag for a CK3 truck build prior to 1/1/85 would be 3 above the red box.
@LS1K501 the second picture is the full page picture. I noticed it has some K1 codes for a 305 at the bottom. I don't know if your truck is 2 or 4WD, but this page will give you a starting point. This is the 9/90 update for reference GM trucks section 8-80. If not on this page it should be one before or one after.
You must be registered for see images attach
You must be registered for see images attach