Chris, uh - no. If that was me, I believe that I said the STAMPED code. The casting date does help a little but only supporting the BW assembly date stamp.
What else do you want? You have no docs and 68s are hard to verify. You document as many original parts as possible - that’s your supporting evidence. It’s most likely a Z28. The parts you have posted along with the production date align with being a Z.
You could hire Jerry M. to inspect, document and appraise the car.