The Stovebolt Site Forums The Shop Area General Truck Talk Engine out, what's this #75 on the firewall???

Well if you go by serial number codes there were 13 during the AD years? This production in some years would have exceeded 300,000 units total.
1-Flint
2-Tarrytown
3-St. Louis
5-Kansas City
6-Oakland
8-Atlanta
9-Norwood
12-Buffalo
14-Baltimore
20-Los Angeles
21-Janesville

Later codes include:
P-Pontiac
W-Willow Run

KMAC