@MeasurementBlues: "There's not much on them that you can't hear on classic rock radio or YouTube."
Ah, but to get the entire album "The Peaceful Side" by Billy Strayhorn I'll have to record it myself. YouTube only has one cut from that album, "Chelsea Bridge," and a cut of "Take The A Train" from a different album. "The Peaceful Side" is a good album to listen to by a roaring fire on cold night with a bottle of Tawny Port.
On the other hand, YouTube does have most all of Quicksilver Messenger Service and Iron Butterfly, but only one cut, "Cod'ine," from Charles Browning's 'Choirboy's Lament.' I have some other vinyl that doesn't seem to be on YouTube, or at least, incomplete (e. g., Pozo Seco - 'Shades of Time').
@MeasurementBLues: "I thought about buying one of those turntables to digitize my vinyl recordings, then realized that the unit would outlive its usefulness ..."
If you still have an analog turntable and a sound card with line level inputs you can get a preamp to boost the turntable to line level. The inputs on a laptop are usually microphone inputs and the signal will be too low without a pream and (I think) too high with one. You can get a preamp with a USB output (see below).
My wife went out and bought one of those turntables with a USB output but it didn't record very well, and the analog outputs were too low (or maybe too high--can't remember what the problem was other than terrible distortion) when I used an RCA-to-1/8" stereo adapter cord, so I ran the turntable through the preamp I bought and adjusted the input and output gain to get a decent signal. I paid $80 for the ART USB Phono Plus at Guitar Center. I'm holding on to my original turntable, a Tecnics Direc Drive with a magnetic cartridge.
This is an extraordinary project that you've undertaken. Ideally these documents would exist in the on-line archives of the various chip manufacturers that made the original devices. Given the fact that many valuable resources are allowed to disappear by their creators, it is wonderful that you've preserved the documents. I wonder whether the vendors could agree to a public posting with clear acknowledgement of their ownership of the material. That would benefit the engineering community, provide free advertising to the vendors, and provide a widely available reference library.