When I was working on my Challenger, I PM'd Larry(hooD) with a lot of questions since his car is fairly untouched and he has some good original pictures when his car was new. One thing that he didn't have was the original voltage regulator. Our cars were built within a week of each other so I was really hoping he would have that info.
I know this is not the voltage regulator but I thought it might help you out. Larry has a really good picture of his ECU on this page.
http://www.cuda-challenger.com/cc/index.php?topic=38653.45It's dated 2712. (271st day of 72) That puts it at the end of September. My car was built in mid October.(12th I think) Larry's car was built about a week later. Hope that helps a little. I just ended up going with a reproduction since I wasn't getting anywhere with the graphics shop that was supposed to be making me a stencil.