Indeed it is. The 'Banbury Set' Mk3s still retain their original doors, and are being painted in the DMU style 'Mainline' livery. As seen in this photo.
https://www.flickr.com/photos/chris...A3d-daKE57-Cneyjf-v5CLNW-xrJptY-BWGe2d-BRHkgR
I was on that set the other week and the coaches were a right mixed bag - some of the "Mainline" livery you mention above, alongside a couple of BR liveried one (including one very knackered one at the front...good for the 68 thrash though ) and an ATW one tagged on at the back (presumably due to the one that made itself into a bonfire the other week)