Key's brass T-1's were available in three different shell styles - the 1942 prototype version and two different production versions ("as built" and "modified"). The "as built" version is pictured above. These eye-catching models are quite rare and, as such, generally sell for premium prices on eBay ($3000+ in some cases). The good news is that they're great runners and might actually be worth the insane prices that Pennsy fans are paying for them (well, very nearly so anyway).
The locomotive chassis is all metal and fairly minimalistic (with most of the model's weight coming from its shell). The motor is a coreless Faulhaber. A multi-piece driveshaft runs from the motor to the rear worm housing. A metal driveshaft connects the rear worm housing to the forward one. Both housings are mounted on leaf springs. One axle per engine is geared, with all gearing being metal. All of the driving axles are mounted in bearing blocks. The pilot truck is spring-mounted.
Right-rail pickup comes from the four right-side drivers. Left-rail pickup comes from the left-side tender wheels, with current then routed to the locomotive by way of a pair of stiff wires on the drawbar (a huge improvement over the old "single wire" drawbar scheme of yore). The pilot and trailing trucks on the locomotive are electrically neutral. As delivered, there are no traction tires (although a TT-equipped driverset is included in the box should you wish to trade pickup for pulling power). A directional headlight bulb is wired to the motor and slides into a shroud inside the shell. A rod of light-conducting plastic then routes the photons on up to the headlight. Wheels are low-profile (no problems on Code-55 rails). As delivered, there are no couplers. However, a screw is provided on the tender for installing a Micro-Trains (or whatever) coupler box.
Paint and detailing are outstanding, and performance is absolutely superb - smooth and whisper quiet, excellent pickup and throttle response, no shimmying or wobbling, and with pulling power to spare. I don't know what the upper limit might be, but the one I tested pulled thirty 40' freight cars like they weren't even there. The minimum radius for curves is right around 15". The only minor issue I noted was a slight bind at extremely low throttle settings (where it's barely creeping along). But that's a small quibble, and who knows? It might just go away after the mechanism breaks in a bit. Overall though, this is one of the finest running steamers I've yet encountered (brass or otherwise).
Note - although gorgeous looking models, I'm told that the boiler shell on Key's T-1 was made slightly oversized to accommodate the relatively large motor. No, it's probably not anything that "Joe Average Guy" is going to notice under normal circumstances. However, place one of these Key T-1's next to NJ Custom's more accurately scaled version and the differences in size do become quite apparent.
To remove the shell, first unscrew the two smalls screws on the rear of the cab. Next, unscrew the chassis screw underneath the pilot truck (just to the rear of the pilot truck screw). The shell should lift off at that point, although it does take a little careful finagling to clear the motor. Note that there are numerous detail pieces soldered both inside the shell and onto the chassis itself, so be very careful when separating the two so as to avoid dislodging any of them.
(Thanks for loaner, Eric!)