The signalling at Preston station which was installed by the LNWR should have been replaced by the LMSR in the early 1940s. But as a result of the Second World War the scheme was postponed, and eventually abandoned.
Two Westinghouse Brake & Signal Company Limited ‘L’ style miniature lever electric power frames were ordered by the LMSR in April 1939.
Frame number 98, ordered for Preston North signal box, was a 227 lever frame consisting of 58 point levers, 135 signal levers, 8 special levers, 12 spare levers, and 14 spaces.
Frame number 99, ordered for Preston South signal box, was also a 227 lever frame but consisting of 54 point levers, 143 signal levers, 11 special levers, 9 spares levers, and 10 spaces.
The Westinghouse Brake & Signal Company Limited ‘L’ style miniature lever electric power frames were delivered as scheduled.
Eventually the frames were relocated to Euston station London, follow link to Euston signal box for more information on the Euston setup.
I do not know of any further information, there is a remote possibility that the Kidderminster railway museum may have a track diagram for the Preston scheme, as they hold all the Westinghouse archive material