In terms of the 50s, in my opinion, Trains Illustrated magazine came into its own and of course remodelled itself as Modern Railways in the early 60s. By then it had started to run articles on the Modernisation plan...hump yards replacing lots of yards based on the pre '48 companies etc. Of course by the early 60s, as has been mentioned elsewhere, many lines had closed, even before Beeching.
The series of articles 'Resorts for Railfans' ran throughout the fifties (I have a list somewhere if interested) but they were all fascinating for spotters and people curious about operations...changing engines, adding and removing restaurant cars and vans, etc to say nothing of trip freights etc.
The TI annual is a good resource too, often running articles about small dedicated lines, special workings, specific industrial complexes etc.(Burton ale system springs to mind!) Now of course, Bylines, Backtrack, BR Illustrated etc delve further. It always amazes me where all the superb, unseen photos of such high quality are found.
So browse a second-hand magazine store/shop...preserved railways will have them to raise funds but the KWVR, vintage carriage trust one at Ingrow near Keighley is brilliant, reasonably priced and very well organised: TIs back to the very early 50s, Railway Observer (superb journal) back to the 40s and of course Railway magazine and World to way back when. They also have most Backtracks, Bylines etc...so
Happy browsing...take a list of wants.
Jim