Beautiful blade! Yeah, nice friend you have there to pass that along!
Maybe the the stampings can help with age if you could figure out what sort of machine the stamps came from. The three circles: Is it one round stamp used three times or a "three barreled" part? The later might make it a bit more unique, as far as machine parts go. Old typewriter parts come to mind...
I can't say I've ever seen a PI blade with stampings before. Interesting work and nice piece!