As for the key feel, it's very unique. It is exponential, the travel starts off very light but then gets super stiff half way through, it's probably due to the leaf pressing down on the dome. It gets so stiff that bottoming out wares my hands out almost immediately. The actuation occurs right as it gets stiffer though, making it really easy to not bottom while typing, I could probably write an entire book on this thing without bottoming out once.
I'm not sure what causes the difference in key feel between these keyboards, it might have something to do with condition but I'm not sure. One useful thing that I've used to identify what switches are in these is the colour of the sub legends, if it's blue it most likely has Mitsumi KKR, if it's red then it's probably leaf springs, this one has purple-ish subs and an italicized font, I don't know if that means that this has a different variant of the switches or not.
These Smith Corona keyboards aren't well documented, so there's probably more to it that nobody knows about. I don't think it goes beyond leaf springs and Mitsumis, but you never know.