You could model modern British mainline preserved steam excursions with a loco picked from your list shown above and a rake of maroon BR Mk 1 stock. You could just run a loco and one Mk 1 brake coach to represent a loco and it's support coach that usually contains supporting personnel, tools and somewhere to brew tea! A Britannia class seen on the mainline is 70013 Oliver Cromwell , with A4s you could have 60009 Union of South Africa in Brunswick Green and Sir Nigel Gresley in LNER Blue. With Flying Scotsman you could have Brunswick Green, BR Blue or LNER green.
If you want to get really serious then most excursion Mk 1 stock coach diagrams are available and you can change the numbers with decals too.
A quick search of Youtube will bring up some interested trains.