Hiya Warmshed, I too have been following the dynamo hum sagas running concurrently, and have been the last few days doing same.
I had 2 armatures and respective fields checked out the other day, and double checked re; connections, as each one I had was wired opposite and both motored correctly(even though one had a stuffed armature the other a stuffed field), so it doesn't matter which way they're wired so long as they motor in the direction of the arrow(in the direction of charging rotation,as you say).
I specifically asked as I figured it would change the "magnetic polarity', but it apparently doesn't matter. Hook up the field and brushes, and if it motors the wrong way, just switch the brushes over and it should motor the correct way.
Also keep in mind that As Trev(?) pointed out that just because they motor, doesn't necessarily mean they'll generate!!!
I had a dud of each field/armatureand built a so far functional one from the refuse(all tested ok with the meter/other tests but the 'growler' said different) .
And don't forget to polarize field connection that's not earthed, to -VE.
someone let me know please if I got any wrong??
Cheers duTch
edited /added this bit... (even though one had a stuffed armature the other a stuffed field)