The spur was between platforms 3 and 4 I think ie next to the inner rail platform 4.
I thought trains were stabled in the city inter peak and I think this carried on well into A stock days too.
I'm going to order myself a grey bobo I think!
There is photo of Aldgate which shows the spur, on Page 32 of John Glovers "Glory Days - Metropolitan Railway" publ Ian Allan ISBN 0-7110-2630-0. The photo is dated as 30 May 1962 and gives a good view of that end of Aldgate.
Of the four that remained in service stock for shunting duties No.1 'John Lyon' (Neasden) was destined for preservation but was found to have a cracked frame and was subsequently withdrawn, that honour went to No.5 'Johm Hampden' (Acton). No.3 'Sir Ralph Verney' (Ruislip) was withdrawn and scrapped after it had served it purpose of shunting the then new 'A' stock in May 1965. No. 12 'Sarah Siddons' (Ealing) of course is still working.
It's odd how impressions from a young age dwell throughout one's life. I was horrified when I first saw a gangwayed driving-end coming towards me. It looked 'not right', as if something had somehow 'escaped', and I still think of it every time I see one today.