What you are looking at is the casting number, C8OF-12131-A, of the distributor housing. The specific number of the distributor as to application (weights, springs, spacers, etc) is the number stamped at the upper lip of the housing, C8TF-12127-F. It's was used on 69 and 70 302CID engines in factory Broncos, not factory Mustangs (Ford Car Parts Sect120 p16).
Jim