Most likely you have the 1963 plate that was issued to your truck in 1963, it still falls under the YOM program as an original plate and some do want to have these black and Yellow plates on their trucks. Under the YOM program, you cannot find another set of 1963 plates and put them on your 1955 truck, only 1951 plates with the 55 tab are acceptable under this program.

1951 Passenger Plate

1951 Commercial Plate

1955 License Plate Tabs for use with 1951 Plates

1951 California Plates w/55 Tab

1963 California Commercial Plates

1963 Plate Designation

All of these plates fall under YOM (Year of Manufacture) Guidelines and are usable if certain criteria is met. They have become very collectable for those who wish to have the original style plates on their truck or car.