It's so detailed that only epochs will do. So forget about liveries, they're on the models anyway.
Pre-grouping - MGWR, BNCR, INWR, SLNCR
Grouping - GSR, NCC, GNRI, SLNCR
Nationalisation - CIE, UTA
Dieselisation - diesels
Rationalisation - block freight, no freight
Each model spread across epochs according to livery