I managed to install the circlips as follows:
1. Work the circlip into the top groove by hand and screwdriver.
2. Hold one end while pushing the other down into the lower groove.
3. Wrap two or three cable this around the fork leg threads to protect them.
4. Have a pair of small long-nosed locking pliers. (Cheap ones) Grind them to a size when they will fit to hold the lower circlip end in place.
5. Press the rest of the circlip down with a flat screwdriver.