There were quite a number of 2-car sets in Scotland, batches of Met-Cams, Cravens, and the original Gloucester type. In the early 1970s the Gloucester driving trailers were withdrawn, and the power cars used to reinforce the others to 3-cars. There were no conductor ticket sales, and this gave extra both passenger and parcels accommodation, and more power to the sets, which had been failures if one engine shut down but just about ok on 3 out of 4. After a while the formations became very mixed, you could find both power cars together with the driving trailer tacked on, and I even recall, idling away in an east end bay at Waverley (so likely the North Berwick service), a Cravens-plus-MetCam twin with one of the former WR suburban-type single unit power cars inserted in the middle. No gangways connectable at all The Springburn to Cumbernauld shuttle was also notable for oddball combinations on the few times I saw it.
It was another of those former WR single unit cars, I think one of those converted to an all-parcels interior, standing at exactly the same position at the east end Waverley bays, when I saw two vehicles numbered the same on the railway - it was car 55015, with Deltic 55015 alongside in the Up Main platform on an ECML express.