The original requirement for the Edinburgh - Glasgow service (on a thirty minute frequency) saw ten Class 47/4s converted to push-pull 47/7s (47701-47710), ten Mark 2F BSOs (9701-9710) converted to DBSOs and 35 Mark 3A vehicles transferred North (7 FOs, 11004-11010; 28 TSOs. 12004-12031). This gave seven sets (DBSO-FO-TSO-TSO-TSO-TSO-47/7) with three spare DBSOs and locomotives.
With a high number of spare DBSOs an additional set was made up using former Edinburgh-Glasgow Mark 2s that had been fitted with disc brakes - 1 FK (13424) and 6 TSOs.
To bolster the loco fleet, however, two additional 47/4s were converted (47711/47712).
It was then decided to operate most Edinburgh/Glasgow - Aberdeen services in push-pull formation so three more DBSOs (9711-9713) were converted (although they didn't receive disc brakes) and they operated with Mark 2D TSOs, Mark 2D TSOT and a Mark 2E FO (there was also a rogue Mark 2F FO, 3284). Four more 47/4s were also converted to 47/7s (47713-47716).
One final DBSO was converted (9714) to replace the vehicle written off after the Polmont accident.
I found the article. 6 sets of 47/7 + DBSO were to be kept for a joint St Pancras - Kettering and Kings Cross - Peterborough peak pool.
The cost of keeping a small pool of incompatible stock killed the idea (the push-pull systems on 47/7 and DBSO were different to what was used on 86/87/90/91 & DVTs).
Plus NSE and Parcels wanted the long range 47/7 for west of England use.
That was probably with the 30 high density Mark 2F TSOs (converted from SOs, which in turn were declassified FOs that had the additional head rest cushions removed). These were split between the Midland Mainline and East Coast Mainline (two rakes for each) as peak busters. If I recall passengers didn't like the high density layout. After the recession of the early 1990s they made their way to the Great Eastern Mainline allowing the remaining Mark 2D TSOs to be removed there.
