Don-
The angled back cap is just a protective cover for the internal cavity. You need a long allen key, 6 or 7mm, I forget at the moment, a "T" handle type works well and the fasteners you need to access are buried in the tunnels, Undo the quill bolt as one always would and tap with a mallet if required. All this trickery was to provide an aero look and save weight. Pino Morrioni did his quill bolt the same basic way, just he did not bother with the hidden bar fixing bolt.
John Jorgensen
departing from Torrance Ca USA