Just so folks don’t get confused, the part number shared by Francis is just the part number for the reflector and not a part number for the housing or the lens.
The tail lights we are discussing were all originally installed on 1967-1971 Alfa Romeo Berlina models, both the 1750 and the 2000. Both styles of tail lights have the same footprint and use the same electrical connector.
The style used by Ford was from the model 2000. This is the style that has three sections, clear, red and red, in a horizontally divided style. There is a European version of this lens using clear, red and amber. The United States department of transportation (DOT) did not allow a rearward facing amber light in the 1970s, but amber was being widely used in other countries. Converting a stock Ford Pantera to the European lens is a simple upgrade that just requires a screwdriver, and hundreds of owners have made this conversion.
The tail lights often referred to as GRP4 tail lights are the tail lights installed on the 1750 model. Again, there were both USA and European versions of the tail light lens: clear, red and red or clear, red and amber.
The GRP4 lens divides the three sections vertically as opposed to the horizontal divisions on the model 2000 style. It requires its own specific GRP4 electrical housing, but the footprint and the electrical connection remains the same. ALSO, while the two mounting studs for the 1750 housing are located in the same place as the model 2000, those 1750 studs are too short to reach into the engine bay and must use 8mm barrel couplers and all-thread (or bolts) to be successfully mounted in a Pantera. Additionally, the two styles use a different black rubber gasket between the housing and the lens. You can FIT a 2000 gasket on to a 1750 assembly, but it is the incorrect thickness (too thin) and you can easily snap off the lens mounting studs if you over tighten the mounting screws.
To further complicate Pantera tail light conversions, all styles were manufactured by two companies, Altissimo and Carello, and while visually very close cousins, the housings and lenses do have minor differences. Almost all of the model 2000 assemblies were made by Carello so there is little chance of miss-matching the components.
But there are multiple examples of GRP4 assemblies made by both of the manufacturers. The Altissimo lens is deeper than the Carello lens, so the divider panels between the three sections are different. A Carello lens will not mount on an Altissimo housing without modifications, and an Altissimo lens will mount on a Carello housing but it is not an good match.
I have sold over 100 pairs of GRP4 tail lights, so I know them inside out. Variations in condition and manufacturing will often have different tones of red and amber, complicating the assembly of a matching pair of tail lights. Not to mention the problems with broken-off mounting studs, lens screws that are rusted in place, and light bulbs that are completely rusted into their sockets.
and now you know more than you ever wanted to know about the tail lights originally installed on 1967 - 1971 Alfa Romeo Berlina models 1750 and 2000.
Larry
P.S. - I do not recommend the purchase of reproduction lenses. Their quality is quite inferior to the originals, being manufactured of clear plastic that is then sprayed with a color tint on the inside of the lens. Originals were actually, somehow, constructed with a thin veneer of red or amber plastic that will not flake off and is easily polished the same as you would polish an aging modern headlight lens.