I would LOVE to see it. Do you have a photo? It would not be "like" the rad support, it would be the exact same font, style and wear as the rad support and cowl numbers.
For what it's worth, this is exactly what I recall being on the original panel. Six digits, identical stamping for depth, font, etc.
Here's why this made such an impression on me, and why I'm more willing to trust my memory for this than I perhaps otherwise would. These kind of numbers meant even less to me when I first bought the car than they do now. I just paid little attention to them. I needed the VIN to register the car, of course, but after that I promptly forgot it.
I was 17 at the time I noticed these numbers, but I didn't really understand them at all. Whenever I was working under the hood I'd seen the rad support stamp and wonder what it meant; I assumed it was a part number. Then I noticed that the trunk stamp was the same, so I knew it couldn't be a part number at that point. One day, for grins, I read the fender tag, trying to figure out what it meant; when I got to the end, and the last six digits matched those two stampings, it was like a lightning bolt. I told myself that I had to figure out what they meant and why they matched. It was about ten years later, after the tail panel had been replaced, before I really started to learn what these numbers were for.
Point of all this is, it's not a casual memory. It was a big deal for me to realize that these numbers were identical.