Thanks, Pete. I really appreciate your suggestions on the benefits of keeping the open frame (OF) motor. Along with the low-end torque, I hadn't considered the added weight of an older motor to increase its tractive power. I'll keep those in mind for any future brass locomotives I might acquire with OF motors.
A quick question for you, Pete: Once you've super-tuned an OF motor, is it fairly quiet? I did run the boxcab as is on DC and it was quite noisy. All the gears - both the gear towers and trucks - are nylon. Since it ran somewhat jittery, I atttributed it to the motor:

Even when I rotate the KMT motor shaft by hand, I can feel the "notches" as the rotor passes the stator.
I did find a suitable "in-house" motor solution that seems to be working well. I have a brass Alco Models FM H20-44 road switcher (ca. 1981) that is awaiting Stanton drives because the gear towers are not worth re-building. I took the Taneda can motor from that, centered and attached it to the boxcab chassis with silicone adhesive, and temporarily hooked it up to a decoder to test drive it:

I would have preferred mechanically securing the motor to the chassis utilizing the screw holes on the bottom side of the motor bracket. Unfortunately, the underframe detailing prevented me from doing that:

The silicone adhesive seems to be working quite well so far. I also use it for securing the metal weights in my boxcar and hopper kits. The can motor is noticeably quieter than the original motor, too.
Once I locate a matching piece of siicone tubing for the other drive shaft, I'll be able to install the decoder and add the front & rear headlights. There isn't enough headroom above the motor for mounting the decoder. So, I'm going to mount it to the nearly flat ceiling of the shell - either to the left or the right of the motor - with 3M foam mounting squares:

I've read that silicone tubing can be had at pet stores that carry aquarium supplies.
Tom