Chris : Just to help you understand the confusion l the hardware part # 40944, a 10-24 x 3/4", hex, washer head machine screw shown in the Assembly Manual for both 1965 and 1966 Mustangs, was not a Serviced Part. In other words, it was a Factory only part. The 1965-72 Ford Master Parts Catalog shows that hardware part # 371698, a 10-24 x 3/4", indented, hex head, machine screw, was the Service Part that was used to attach the bars to the corral.
Hope this helps,
Bob