Big yellow train

At first I thought it was advertising Yellow Pages, but it was Network Rail 'Improving your railway.' There was a Class 37 loco at each end. There was also an electric drive unit, which looked to me to have once been part of a late lamented class 303 'Blue Train.' I base this on the refitted windows of this type which many of these trains got in the late 80s. See extra shots. All at Inverness Station, yesterday, and I was the only train spotter.