I haven’t had a lot of luck finding a suitable donor keyboard in the thrift shops lately so that may have to wait, but I have devised a suitable alternative plan which I will definitely share with you when it’s done.
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The CMOS kbd encoders 74C922 (16 keys) and 74C923 (20 keys) are, in my mumbling opinion, the best choices. Make a simple R-2R DAC to get a CV. The chips has a strobe output that can be used as gate/trig.
I have seen keyboard designs based on any of these ICs but cannot find any link right now, but it shouldn’t be hard to put something together.
Another solution IF the keys have a common rail and cannot be used by scanning is to use a priority encoder. I have somewhere started building a simple keyboard using TTL chips (74147). These, like the CMOS kbd encoders provide binary outputs and strobe.
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Thanks for the input. I have a few 74C922 chips due from AliExpress in a couple weeks and then hopefully I’ll be able to slap something together over a weekend.