That big screw on the case holds the field coil in place. It screws into a magnet inside the case, and the field coil is clamped between the case and a lip on the magnet. I would not try to move it unless you need to remove the field coil. The hard bits in reassembly are the brushes. I just use a skinny zip tie to hold them back against the springs when you slip the armature back into the case. Pulling the bushing from the end plate, I use a tap and a bolt. That gives you something to pull on when removing the bushing. That and the connections is about all there is. The Armature has what is called the commutator. That is the brass part the brushes sit on. You can clean that up with some sand paper Just like the book shows. The insulator cut back technique in the book is easy with a cheap set of jewelers files. Dirt, brushes and bushings are the usual bad actors. Bendix drive is common to.
