I used to know the alloy of the stainless? I think it is 21-n which is used for the severe duty racing valves.
That market is so competitive that they stab each other in the back all the time and because they are manufactured overseas don't have exclusive rights to any on special brand names.
FYI, EPN told me they ARE made here in Las Vegas but there is so much of the "alternative facts" syndrome, that it is confusing.
Bottom line, you have what are PROBABLY the best valves you can buy.
In the "old days" we would just copy as best we could of what the big name drag racers would do.
They blew up everything under the sun and whatever they found to be the most dependable was the way to go. It saved a lot of expensive experimenting and actually educated us pretty well.
It was always amazing to me that a guy like Bob Glidden was just a regular mechanic working at a Ford dealer in his regular day job? It just adds to my confidence in questioning authority or guys at the top.
Incidentally, those valve guides are used by just about every aftermarket head manufacturer. I think they are the best available and use them too.