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They do have a metal insert. When the plastic wears away the metal starts to scrape against the side of the keyway, telling the user that they are due for replacement. Are they identical to Yamaha or Jupiter guides?

I don't have an Eastman.
But I have a horn where I wanted replacement valve guides.
Took a couple of images of the guide.
Then took a couple of measurements.
Sent this information off to a retailer of spares and they let me know that they had them in stock.
Worked out fine.

I have Yamaha felts in my Eastman and they work fine. I'll bet the guides do as well.

Yamaha valve guides fit the Eastman pistons perfectly and appear to be identical to the originals.
I also tried a Jupiter-style valve guide. It does not have the metal insert and did require a bit of filing to make the post fit into the tiny hole on the top of the piston, but it does fit and works well after that small modification.