As far as I know loft, lie and length. I assume there're nearly identical, just that one had a "1" stamped on it and the other a "3"
I'm no expert on the history of golf equipment, but I seriously doubt that.
When pros were asked to hit Hogan's old clubs, one asked about the 1 iron, "What’s the loft on this—zero degrees?”
I read where it was actually a 17 degree. Leaving that aside, I just don't see how anyone could make a claim that older equipment is equivalent to today's equipment, in any way.