I grew up in Huntingdon and went to school at Hinchinbrooke which started my interest in trains as the Lower School was the opposite side of what is now the northbound car park.
IIRC around 77/78 we had Cleethorpes and Leeds stoppers northbound, mainly 47/4's, (usually FP and GD with the occasional HO). I haven't a clue where the southbound ones came from but assume the same. I don't ever recall direct trains to York but there may have been a few- every time I went to York we always changed at PBO. Deltics stopped less frequently until the HST came along. There was also a smattering of 31 hauled stoppers with Mk1's, presumably only going from/to PBO in the morning and evening peaks. 40's and 46's were also quite common but I never remember seeing one stop at Huntingdon. There was a northbound stopper around 0850 - just before the bell rang for school that often produced a more exotic foreign 47- CD and even an LE allocated on more than one occasion (?)
Freight was mainly 31's with a handful of 47/0's, 40's and 25's.
The favourite train for London spotting trips was a PBO- KX which left Huntindon at about 0750 and got to KX about 0900 with one stop at St.Neots unless my memory is failing.
I remember the DMU services to Hitchin all too well- to be avoided at all costs if on a spotting trip to the smoke although I vaguely remember taking one all the way to Welwyn GC to see the 313's when they first came in.
As mentioned before, the end came when electrification arrived and the 312's took over.