All of this generation of coaches shared a lot of components, particularly when they first appeared. On introduction in 1977 there was a Compo and Brake Third for the LMS, GWR and SR and a Compo and Brake Compo for the LNER. All shared the same bogies (a clip-in variant of the BR1 still used on their current Mk.1 range), floor unit, metal weight, glazing and two patterns of interior, a composite and a brake, the latter arranged to 'sort of' fit all the brakes despite the varied number and types of oompartments modelled. There were also some components shared over parts of the range: the GWR & SR shared coach ends and the lower part of the bodyshells (the roof part of the shell was different so they must have had interchangeable roof detail tooling). Later the LNER coaches gained Gresley bogies and after that the GWR coaches were given 7' bogies. Incidentally, both the new types of bogie slightly lowered the ride height compared to the old BR1.
The GWR Restaurant car and Gresley Sleeper obviously had new bodies and interiors to suit, but the other parts were still standard (and both gained the better bogies later).