Yes I know about the growler. My '54 Olds has a generator and the only way to REALLY test the armature is on a growler. Years ago these places that rebuilt starters and generators all had growlers. Without the growler, the best way to read low resistances is with a Simpson 260 (which I also collect!) but this is a rudimentary test.
I have other similar motors around I am just going to swap some stuff out if necessary. If this turns out to be something really stupid I am going to feel like a real dummy...