It's the keyboard for an
IBM 5251 Displaystation. I'm typing on one I received this week and just finished cleaning, funnily enough
dgneo is correct, a beamspring xwhatsit will convert it incredibly easily. You'll need an extra controller to drive the solenoid if that's something you're interested in, but they work just fine without it (I'll probably add the solenoid controller to mine eventually). Just unplug the original controller and plug the new one in, no soldering required. Programming is very easy. Just need to watch the ergonomics, it helps to sit high and have your desk low! Ellipse may still have one or two controllers kicking around:
http://www.modelfkeyboards.com/product/xwhatsit-beam-spring-or-model-f-controller/These are a bit more common than other beamsprings, lately a few have cropped up on eBay. But make no mistake, they are almost certainly the ultimate tractile, clicky switches ever produced.
