Back in the 60s, there was a regular DMU turn from Newcastle to Leeds, 2 return trips a day. I used it to York a few times as cheap excursion tickets were available, but York was too far for a cheap day return and an ordinary return was stretching pocket money more than a bit! It was usually a Met Cam (later class 101) 4 coach set, for at least 1 timetable with a buffet included, but I remember all types including Derby lightweight sets being used.
Once, I saw the evening train leave Newcastle on a particularly foul snowy night, with an A4 on 4 pre nationalisation coaches.
An interesting point is that, even with their 70 mph max, they were routed fast line all the way from Darlington to York (Thirsk retained fast line platforms in those days). Back then, there was a steady procession of freight on the slow lines.
Another long DMU turn ws a Saturday service that arrived in Newcastle from Doncaster, which was diagrammed for a Calder Valley set.
Back in the summer of 67, I had a few journeys from Peterborough to Newcastle on the 18:05 ex Kings Cross (Having watched the Deltic on the 18:00 bowl through without stopping). I would bail out at York onto a DMU that followed it to get home quicker, as the 18:05 was routed via the Durham Coast. I remember that I used to find a seat in a trailer vehicle as I was too tired to put up with the engin noise under me.