Ah right, planning to do a model railway based on an area where a Central 170 and a VT HST would've been (only two pieces of stock I have).
Bear with me here but, Hope Valley/Nottingham/Derby/Sheffield area?
When Virgin finished with their HSTs, they were used by MML to run from St Pancras to Manchester via Derby and the Hope Valley Line (Project Rio), at the same time CT 170s would be running Liverpool to Norwich via the Hope Valley and Nottingham.
This gives a few options though and interesting formations. In the early days of Project Rio the coaches weren't all ready, so short formations were the main, then as coaches appeared so did the new livery they adopted and some sets were seen with mixtures of Virgin, MML Teal & Tangerine, and that new white/blue livery. Although the Rio sets never had the Virgin livery on the Buffet car.
Formations could be as short as:
PC-TGS-TSO-TSO-TSO-TFO-PC
This video of my layout shows my Project Rio HST: