As a general rule, no, not really. Most of them have a specialized L head gear train to support the wheel. The bearing set is in the gear head. If you go through the trouble of reworking the motor with a new end plate and bearing mount you still have a motor that was not meant to run long term without external cooling. And most of them have brushes that will fail in fairly short order under constant load. On the plus side, they do make excellent coil winder motors. With a beefy PWM circuit you can wind the largest magnet wire you would ever want into a tight coil. Just be sure to understand the tension requirements for the wire gauge you are winding, I have used an old Baulder motor (geared down) to drive a pipe bender. You can snap 10 ga. wire with one of these without working it hard.
Whatever you do, don't try to reverse drive the motor long term through the gear train. If you get it to turn, it will do ugly things to the gears in short order. With most of them, reverse gear train drive is meant to be a system brake.
