I worked on this in about 1995, concurrent with working at London Bridge on the JLE for the same contractor.
very interesting job, although plagued with delays and litigation from the "heritage" people on the one hand and changes to the design ( due to changing the loading gauge at low level to clear the bogies on main-line stock ) on the other
''the stopes soared beyond the range of our caplamps' - David Bick...... How times change .... oh, I don't know, I've still got a lamp like that.