That's the main culprit. Quite a lot need little work other than
stripping/resurfacing/drainage cleaning. WJ is the difficult one to squeeze
another car length out of. Even SDO (to use the inner doors only of the end
cars) wouldn't work, due to the siting of the signalling.

Pardon my ignorance, but what signaling problems would affect the use of
SDO, such as not releasing the doors in the rear coach?