It's been a long time since I've worked on a 516, but I'm thinking there may be a small set screw that keeps each brush holder in place.  If not, then when you remove the long field screws and then the field itself, the brush holders should just pop out.  Those brush holders are the same as the ones on older models, so they're probably held in place with the field screws.  In fact, I just went and looked at the photos of your previous post and noticed bolts on the field screws, so that tells me the field screws are used to secure the brush holders in place.  THEREFORE (LOL!), they should just pop out.  Have you tried reaching inside and pushing them out?  (sorry for the rambling).  As for the armature, the only thing that really needs cleaning on it is the commutator (the round brass part at the end).  You can use something called a commutator stone.  I've included a link so you can see what it looks like, but you can order it much cheaper from A007Kirbyman.  The stone is used to clean carbon buildup off the commutator and also the seat (or shape) the brushes onto the commutator.