The BR Class 50 is a british diesel locomotive, built between 1967-1968. Despite being over 50 years old, these can still be found on the mainline today, although a rarity, along with a few heritage railways, most notably the Severn Valley Railway. I think many people would love to have the Class 50 in TSW 2, especially in an NSE livery (like pictured above), possibly making both NSE liveries, or the BR Large Logo. I'm sure the thought of letting the Class 50 loose, full throttle would really appeal to many TSW 2 users.
In the early 1970s I used to see pairs of them in BR blue double heading the London Euston to Glasgow trains out of Crewe. That stopped once the line was electrified and the 87s took over.