I found similar markings on my 15,000 mile car. Mine had 2 inspection tags on the heater box and had similar grease pencil number. My understanding is the handwritten number is an assembly sequence number. Mine had a "3" and I found the same "3" on top off my gas tank. I did not find any yellow tape. Steering column and gauge cluster tags are the "norm" for identifying applications for those components.
Sounds like you have a really cool Z - post some pics!