I don't believe these had any kind of smoke, but there's plenty of room to add one and there are a lot of good choices today.
I would *definitely* add a flywheel if the loco doesn't have one. Coasting is important, especially with four rubber tires and self-locking gears.
The factory motor is OK but it does draw a lot of current. You might find a Pittman 9000-series motor to be too slow-turning by comparison. The smaller 8x24-series has a no-load RPM closer to the factory motor and is still plenty powerful. My $.02.