The "missing door trim" was a dealer-installed (or owner-installed) item. The car looks much better without it, but I'm sure it helped fend off a lot of door dings over the years.
8" snowflakes means it should be a WS-6, and I don't recall if you could get that package with the Olds engine or not.
The "Z" in the VIN indicates a 400cid Pontiac. A "K" would have been the 403 Olds engine.