The SRS do seem to have some interesting stuff catalogued, mostly relating to the WCML resignaling scheme's prior to the putting the knitting up, I have collected a few of the issued documents 1G, 2G and 3G, but always nice to see some of the planning documents. Alas, the Carlisle PSB train register doesn't appear listed.
Managed to procure the below:
I'm hoping that I might be able to eventually come across the May 1974 W2, which someone may have saved because of the Royal Train's visit to Preston on the 6th of May 1974, for the Queen to unveil the plaque to mark the completion of the WCML electrification among other interesting events. Such as, 25233 and a saloon being used to transfer the Queen from Preston station to the new Preston Power Box, and the Queen travelling north to Carlisle in the cab of 87018.
Regards