It seemed daunting to have to pull out the dynamo just to change the brushes on my C35 so I have found it is possible to change the brushes in the car with the advantage that the timing is not disturbed at all.

By unscrewing the two long bolts down the length of the dynamo body (from the distributor end), the dynamo can be pulled out about 2 cms. Which is just enough to clear the locating pin and allow the body of the dynamo, with the distributor still attached, to be freely rotated so that one can get at each of the three windows in turn and replace the brushes without having to delve underneath or next to the radiator.  A bonus is that the distributor also rotates without leaving the gear at the end of the armature, so the timing is not altered at all.

David Whetton DA7C