You will want to print the key upside down if you don't want to use supports.
With these old machines having not been manufactured in the last 30 yeares, spare parts are getting impossible to find. So I disigned this key to replace my arrow key that was missing. I have also included the Blender files so you can modify the key to your needs.
The Mounting point fits without any futher machining needed, however if you need to remove the key again, the peg will snap as it has a tight fit, so make sure you are ready to install to save you having to take the key switch apart to remove the peg, it is a pain in the ass.
Hopefuly this helps you restore your vintage computers as well. More obsure machines like this sadly don't have much models at the moment.