The Roadster Factory sells these plates, ready to go, just like the original. You will need a letter and number punch set to stamp in your numbers (serial, build date, etc.) I would advise getting a scrap piece of aluminum the same thickness and practice, practice, practice before you tackle the new plate. Oh, and the obvious, stamp the number on a good hard surface, the the fender of your car. Sorry, I had to say that. One guy actually did it that way. What a mess.
The plate makes a nice touch to the engine bay. My car (1973 TR6) had the engine bay plate (I put a new one in.) as well as the holes on the B pillar for the other plate, but none was ever installed. TRF sells these too. (they are slightly different, I think) I got so good at stamping numbers, I added one here as well.