That link's great for the part numbers. I heard it's getting easier to get a second mortgage so we may get some replacement gears at some point. Joking apart I was surprised to find most of the bits are now available new from the usual sources. I'm pretty sure they weren't in 1980 when C Manning bought 3 spares 'for 30p' (FYO p205)
'Forty Years On' is extremely useful but somewhat sparse of drawings (and the typeface harder to read than the recently criticised captions in MPH). Here's an article I found on the Burman box which has lots of line drawings.