When out shopping... anything specific to your '51 will carry a 1A prefix. The parts carried over from earlier models will almost all have 8BA or 0A '49-50 parts prefixes. '49 is "8" because it was planned to be released as the '48 Ford.
The piece you have is an old replacement part from the aftermarket. The HLR451C likely means "Head Lamp Rim 4(Ford?) 51(year) Chrome" followed by the original FoMoCo number 1A-13045 described by Ford as headlamp door.