I was loath to do this, but curiosity got the better of me. I stripped the 1st, the 45 deg unit. Pick ups and carbon brushes out, remove 3 screws holding the body end plate, and lever end plate off, over the bearing. Slip ring now visible, but bearing inner ring needs to come off first. Specialist bearing pullers were made by magneto firms years back, but I don't have any, so compromise was needed. I found my 2 leg bearing puller, found an engineer's clamp to stop it spreading, and tightened both with the puller engaging with the groove in the bearing ring. With some soft packing between the screw and the taper, the ring slowly came off. The slip ring was a slight interferance fit on the shaft, but came away fairly easily.
This exposed 4 screws holding the core end plate to the core, these were carefully removed. With a few light taps from a punch from below, the end plate came off the 2 alignment pegs and it was in my hands. I then moved on to the 2nd magneto. All went well until I got to the slip ring. Unknown to me, this was a genuine Bosch component, the other had been a modification! The slip ring shattered, and left a plug of material in the hole where the wire exits the winding and finds its way to contact with the brass segment in the slip ring. After further persuasion, this plug came off, and I could remove the end plate as before. I then swopped the tapered end plate with the spade end plate, so I at last had a 60 degree magneto with a taper shaft for the sprocket.
Unfortunately, I now didn't have a slip ring for this mag!
So, out comes the 3rd mag, and another strip down, to remove a genuine slip ring so that this could go into the mag with taper shaft - no mistakes/breakages this time!. One complete mag suitable for the prototype!!!!
Searching on the interweb, I found: http://www.themagnetoguys.co.uk/slip-rings
just below the centre of the page is a photo of a stripped Bosch slip ring. They were made in 3 pieces, part of it being screwed together! I found some super glue, and set about reconstructing my shattered slip ring, but one large piece is yet to be found. I may attempt to make a new one, or I may get one of the restorers to make me an extra one when I get the mag professionally rebuilt.
Shame the older chap didn't warn me about the screwed on slip ring!
Please don't make the same mistake if you have a Bosch magneto of a similar age!!!!