Some may be sick of LNER locomotives, as they have much more of them in TSC compared to say, Southern Railway engines, but I think one major workhorse of the GNR that would be interesting to see (& useful for 20s–50s scenarios) would be Gresley’s K3 Class mogul, originally known as the H4 Class. They were employed mainly on mixed duties, but later on mostly found work on freight trains. They were built in many locations LNER locos were constructed, but most were from Darlington, although they were originally native to Doncaster. They acquired the nickname of Jazzers due to the lilting sound of their boiler. The first of the class had entered service in 1920, at the twilight of the GNR, but were built well into LNER days, ceasing production in 1937; they lasted in service until 1962. Although none were preserved, the A1 Steam Locomotive Trust (builders of Tornado) plans to build a new example as their fifth project. I think these engines would be a good choice as they were on the primary ECML roster from their birth to their end, working a variety of trains and representing the pinnacle of GNR locomotive development.
Not just up to the 1950s, they were still in fast freight and excursion passenger traffic up until at least 1963. Ideal engine for the Netherfield route. Edit: In 1959 Colwick shed had 13 allocated, in 1963 it had 17 although some were in store. They were used on fast freights to London and Sheffield and were a stalwart of the summer weekends for excursions from Nottingham to Mablethorpe and Skegness. In 1963 Colwick became LMR property and the excursions from 1964 were hauled by LMR engines and the ER engines were rapidly replaced by Black 5s and 8Fs. Ah, I remember it well, sitting on the wall at Netherfield next to the Bourne factory. The pinnacle of GNR loco development were the A1 pacifics but the K3s led the way to them.
