Sorry for the long hiatus; life go in my way... *grumble*...

Anyway, I solved my problem, sorta:

I since found a Sprint P8767, which fully activated and worked on both CDMA 800 and 1900, so I can get service everywhere with it.

What I ended up doing, because I like the styling of the older black plastics better (the P8767's stock plastics are kinda gaudy looking to me), I took the main and keypad boards from the P8767 and transplanted them into the old ST7867 body, which worked because the P8767's innards are mostly identical (the displays are different). So, I now have a lovely black StarTAC that works everywhere my smartphones work!

I'd still like to solve my original problem, though, because I like the original 7867's blue backlit LCD better than the P8767's green OLED display, which was necessary to keep because the P8767 won't function properly with the 7867 keypad.

There's the Talkabout T8367 that is basically identical to the P8767 in terms of features, but it has the traditional blue LCD of the 786x, but I couldn't activate it, even though it was a Sprint model, because for some bizarre reason, it's ESN isn't in their database (and, since CDMA is on its last legs, they won't add it, so it got blacklisted instead). I figured that I could clone the ESN of a phone that does activate onto it, but not only is that illegal (why would it be so wrong for a 20 year old phone, though?), I don't have the means to do it.

Oh, well, I'll take what I can get!