These are, without question, some of the most amazing brass models it's ever been my pleasure to try out. What's more amazing to me is that they came out in the 1980s (a time when, let's face it, there weren't a whole lot of really amazing locomotives available in N scale).
The shells are nicely painted and finely detailed (separately applied handgrabs, etc). But it's the mechanism that really blows me away. All wheels are geared and provide pickup. The motor is an amazing little 5-pole affair, allowing this thing to creep along at ridiculously slow speeds (while at the same time making for a very reasonable top-end speed). Better still, all of the moving parts are (apparantly) plastic and work together beautifully. This model runs as smooth and as quiet as any modern Atlas or Kato diesel loco. On the downside, pickup is provided by wheel-wipers and current is moved around via a whole lot of wires. But given the overall wonderfulness of this mechanism, I'm willing to cut them some slack on that particular issue
The real topper here is that the "A" units come with honest-to-gosh directional LED lighting. I'd say that about 90% of the brass locomotive models I've ever seen didn't have any lighting at all, let alone directional lighting. So, wow, what an amazing feature to find in an old model from the 1980s. OK, the light is green (of all things), but I suppose that's probably due to the limited color options available in LEDs "back in the day".
All of the Key FA's that I've ever seen had Micro-Trains couplers installed on them. I don't know if they actually came from the factory so equipped, but it seems like maybe they did (again, kind of odd for brass - most of which don't come with couplers at all). There is actually a premanant drawbar between the "A" and "B" units (as opposed to couplers). I believe this is normal for these particular prototypes. These were generally sold in A/B sets (with both units powered), although A units were also available separately.
To remove the shell, find the miniature screws underneath the trucks (two per truck) and unscrew them. The shell should lift right off at that point. And once more, I have to question the sanity of the dude who decided that hiding the screws underneath the trucks was a good idea...
Here's the "early" FA-1 -