arjaybe: I have a Thinkpad, but it's a Lenovo, not IBM. I think the keys have scissor switches. It's an oldish one (about 7 years, I think) and has the traditional Thinkpad keys, not the island type. I always liked the keyboard, until some keys stopped registering. I hate the style of the new Thinkpads; if I have to buy one, I'll use an external keyboard. What you've said about the Unicomp is more or less what the keyboard reviewer said:
https://www.youtube.com/watch?v=-A-vRZth7SI
I just wish they made a TKL version.
As I've said, the electric I had (and still possess, but the A dropped off) was a Smith Corona Electra Automatic. They're frequently available on ebay, but useless if the typing can't be transferred to a laptop. I tried to lift it recently and was amazed by the weight; it's heavier than the two laptops I have put together.