Success! I used the "strip away old insulation and slip new larger diameter insulation over it" method. I replaced all the other wires, opened the motor and reversing switch, cleaned and lubed as needed - tested and working well. Brushes are in good shape, I guess this doesn't have that many hours on it.
@BMORAN4 Regarding the back side of the collector plate: "It is nothing exciting - just the other ends of the rivets - one of them has the lead soldered to it."
(I seem to have trouble quoting, will figure it out later.) Ahhh, seems obvious now (which I guess is why no one bothers to post a picture! 
). But that got me to thinking, if someone needs to replace the rollers/copper plate, and/or the pickup wire - I think it could be done w/o going through all the problem/risk of spreading the frame. I'm assuming that in most cases, the insulator plate itself is intact (or could be repaired in-place with epoxy). Does this sound reasonable? Procedure:
A) Drill out the two rivets. Lift off nameplate and conductor plate and set aside.
B) Drill an ~ 1/4" hole (or slot) in the center of the insulator plate (will be hidden by the conducting/name plates).
C) Push a new wire through that hole, fishing it up to the reversing switch. Strip 1/4" at the plate end, tin, and bend into a "V". Bend at a right angle at the insulation.
D) Solder this new wire to the conductor plate, right over where the hole is, so the plate will sit flush.
E) Fasten the plates with two small self-tapping screws.
I'm assuming it won't be too hard to fish that wire up to the reversing switch, but I don't know w/o trying. Opinions?
Since my roller plate is kind of bent up, I think I'll buy a replacement from one of those listed sources, to have on hand if it breaks. I'll get a new front pilot truck at the same time.
