It's a Mitsumi Quick Disk! The kind that was adapted into the Nintendo Famicom disks. I should have remembered that Smith-Corona used these drives for some of their systems.
Anyway, this is a Smith Corona PWP 220.
And our firmware is here, on an AM27C256 EPROM. 32 entire kilobytes.
And it's yet another eprom soldered to the motherboard, argh.
They wouldn't have room for a socket here (because it's under the shield) but they could have shoved it over on the left, where there's no shielding, surely?
There's a big chip from Motorola that says 761060 SCQ38124PI01 ZQHAE9102
No results, but there's a reddit post speculating this is some kind of IO controller. Possibly this is a custom ASIC, I believe Motorola had a product line for making those, as a sort of proto-FPGA service
Found an ebay listing for one.
https://www.ebay.com/itm/295124046576
The back of that monitor makes me think that yeah, it's an MDA monitor. Definitely not color.
Did one of my trademark High Quality Pinouts for the keyboard connector.
it seems it has a 4-bit or 5-bit interface. My guess is that it's a 4-bit IN and a 1-BIT OUT. Possibly just a shift buffer on the keyboard side, and the OUT is used to trigger it to read out another 4 bits?
@foone wild guess: that's a TL431/432 in the pic near the FET.
Pretty common to build linear regs using a big series device like this with a high gain reference device like the 431.
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William
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Kevin Karhan 
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