If you go to this link you can see there was a batch of 1108436 starters made for the 1973 SD455 program that were all made in 1971 on a certain date "1B11".
Your starter is a 1973 date "3B63" so it could be for a regular 455 for 73 or an over the counter replacement for an SD-455.
https://www.yenko.net/forum/showthre...er#post1337174