I took a shot of 33058 bringing an oil train from the BP terminal through Princes Risborough - would this have passed through Aylesbury? same day as my other post - 24 May 1980. It's quite a long train.
Can't upload it at present - let me know if it is of use to you and I can email it or post it later.
I took three photos of signals at aylsbury on 24th May 1980.
One of these shows a number of DMU vehicles stabled as described above.
Hope these help with your model.
Thought you might be interested in this working which I believe was a regular occurrence on the line - taken
01/07/80 at eggesford , a 3 car dmu with GUV tail load. Morning working I think from memory.