The way we used to adjust valves on the first water pumper VW's (Rabbits & Dashers c.1974/5) was to use a hand held, Y shaped spring compressor to push down the bucket. Then, we plucked the shim from there with "pliars" which looked much like snap ring pliars with about a 30* bend on the long, skinny ends.
Isn't there enough room on top the twin engine head to do this? Seems like a real pain to remove the cam bearing caps!
From the pics posted above, it looks as though this method could be used on the outer valves, but maybe the inner ones are too "buried".
