Had a bit of a senior moment there, of course they did, ignore me! Was heading south-west-ish from Dundee, mid week, with a 26, possibly late afternoon time (dusk was encroaching whilst 'on depot', that I do remember, prior to departing Dundee - April 81 period). It may have been possibly early (morning peak sort of time) the very next SX day, but notes/workings etc all lost. A change of train was made en route to Glasgow, in to a service headed by a Brush 4, so possibly at Perth, but other than that, no real clues? Just trying to identify the trains concerned I guess, but appreciate too many variables to come to any realistic conclusion.