More sensibly, given the length of time it would have taken to load/unload while blocking the main line, they split the overlong trains at KGX and drew forward everywhere else.Back in them days, people would simply use a bit of common sense and alight and board the coaches that were on the platforms. Simple.
In 1960s the fairly usual number of carriages on trains on WCML was 12 for Euston to Manchester, Birmingham and Liverpool...
Actually slightly shorter than an 11-car Pendo, even with the loco, and certainly seating fewer (cue comment on comfort...)