And if I keep the keycaps, I'll want some replacement caps for keys with black legends that I don't have (Num Del, Ctrl and Alt). I'm not getting them from Unicomp as I don't like how inconsistent they can be. I could get a perfect cap, or one that's off center with burrs and the wrong color subtext.
I guess you could make them yourself, but I suspect your own results will be more inconstant than unicomp's. Who, other than Unicomp makes custom IBM keycaps?
I have a LOT of IBM keycap sets and they are already inconsistent. They changed their line width sometime, as well as some other things. In many ways, unicomp's keys are more consistent and clearer (less "fuzzy" than IBM's.
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As far as valuable, I try to only pay $30 or less for "special" IBM keycap sets, and I have 3 or 4 now. Are they rare? certainly: Lexmark almost certainly did it as a custom order for a customer. Valuable? probably not any more so than other custom sets, but (as always) it depends on the buyer.
I know that over time, IBM was very inconsistent, however, if I buy from the community, I can get pictures (and descriptions) and weed out the ones that are not what I want and pick and choose the ones that fit the need.
Even with the consistent keys from Unicomp, they would not be the same consistency as IBM had (blurry legends, different shades of ink). A whole keyboard of Unicomp caps is great, but even between Model F and Model M, I can't just swap the F and J keys around because they have different printing thickness, width, etc and a different texture all together. I'm too picky about it...
I'd also like to see photos of your custom caps. I always enjoy seeing unique things just for the sake of it.
On a side note, I looked at one of my Ms and it had the exact black legends I needed. I'll certainly be getting caps from Unicomp in the future (blanks, colors, side printed F keys), but not ones that need to be matched up with IBM keycaps.