Just picked up what appears to be an IBM 104-key "space unsaver". I believe it's the model F one (not the rubberdome one that's been on ebay forever)
Unfortunately, it's the much rarer part number that actually starts with a 6 (the post with that info appears to have been lost) so I don't think it's compatible with a modern computer.
Actually, there was almost no information about it, so I hope it's all good.
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In his message, the eBay seller said he has two, so I guess I'll take both.