And did you discover that by scraping off the black outer coating, the OC71 could actually be used as a crude photo-transistor? [Linked Image]

I think the switches you're referring to might be the same ones that I used for many projects around that time. They were round and silver, not much more than an inch or so in diameter. Although looking like a miniature tumbler switch, the contact action inside was just the operating dolly pressing down on a copper strip.

I also recall that the outer shell was also connected to one side of the switch, a fact which I think I only realized after dropping something across two switches which were on opposite poles of the battery!

I do remember that I ended up using loads of those little switches on my model railway layout.