If you want to take that barrel off, it's not too difficult to get it back on again. When you undo the two screws at the end and pull off the end piece the two brushes will spring toward the center. A good way of reassembling the motor is to slide the spring-loaded brushes all the way into their carriers and secure them with a long, skinny strip of masking tape. When you put end piece back over the shaft , the tape is holding the brushes out of the way. And then when you get the commutator (copper segmented ring) between the brushes, you can loosen the tape and pull it out, allowing the brushes to spring against the commutator.
Probably the harder part of all this is to get the two windings out of the barrel. They are held in place by those big screws in the middle of the barrel, and those screws are usually rusted tight. So if you're going that far, you might have to be prepared to drill them out and repace them with others (1/4" countersink heads, I think) Good luck. Let us know what you ended up doing.
