Which was done last, Cowl white or firewall blackout on Z

[BillOhio]

If I am understanding this, there shouldn't be primer over the paint. So this over spray shouldn't be primer. Eddie believes this is stripe over spray.

[ZLP955]

No, it appears that there is a black (more DEEP chocolate) paint or some type of coating applied before the grey primer and before paint, thus would have been before any final finishing, some cars do not appear to have had a final black out done to the firewall.
See it here under the gray primer and black overspray.

Isn't that the phosphate coating described in JohnZ's assembly process article?

[firstgenaddict]

If I am understanding this, there shouldn't be primer over the paint. So this over spray shouldn't be primer. Eddie believes this is stripe over spray.

Yes that is correct it is stripe over spray, there is a picture in Jerry's book which shows a 69 Z with a completely white firewall from the wiper well white out.