These two models (J-1 and T-1) came out at the same time, so I'm going to go ahead and assume that they both share the same basic internals.
The locomotive chassis is all-metal and fairly minimalistic (with most of the actual heft being provided by the shell) -
The motor is a closed-sided can (Maxon #118411). The driveshaft consists of two plastic U-joints holding a telescoping plastic tube. The motor and worm gearbox are mounted on a sprung torque arm. Only one driver pair is geared (the fourth pair from the front). All the rest of the drivers are turned by the cranks. All ten drivers are sprung, which presumably makes for quieter running and better contact between the drivers and the rails. The driversets are seated in bearing blocks that mount inside cutouts in the frame. All gearing is metal.
Right-rail pickup is provided by four of the right-side drivers. The #2 driverset is equipped with traction tires (a non-TT driverset is included in the box should you wish to trade more pickup for less pulling power). The #3 drivers are flangeless. Left-rail pickup comes from the eight left-side tender wheels. The tender trucks are both spring-mounted. Current is conducted from the tender to the motor via a stiff wire firmly soldered to the drawbar. A non-directional headlight is wired to the motor and mounted inside the shell. The pilot coupler is a dummy (non-operational) knuckle (although it does pivot). The tender has no coupler, although a MT-friendly pocket (with pre-drilled hole) is provided. Wheels are low-profile, so no problems on Code-55 rails.
These are fantastic looking models that perform quite admirably. Mine runs extremely smoothly and quietly. The top-end speed is quite reasonable and the low-end speed is definitely "one tie at a time". The only minor issue I encountered is that it does exhibit a very slight bind at the extreme low end of the throttle (perhaps due to the quartering being slightly off?). Whatever the case, it's a minor annoyance at best and not anything that I'd bother trying to address. Despite the old-school drawbar wire, electrical pickup and conductivity are flawless (no stalls, no stuttering, no problems creeping through turnouts, etc). Mine can effortlessly pull thirty assorted freight cars through curves on level track, so pulling power is strong. I have no idea what the absolute upper limit might be, but it's gotta be well over fifty cars. Mine cannot handle 11"-radius curves (the tender consistantly derails), so 19"-radius is probably the realistic minimum for these locos.
To remove the locomotive shell, first unscrew the screw underneath the pilot truck. Next, unscrew the two small screws on the back side of the cab. The shell should lift up and off at that point. Just be careful not to dislodge the headlight wires that run from the motor into the shell.
A PRR J-1A was also part of this release. Note the different tender -