Sorry I'm late to the Bristol Poly reunion - I was there at Unity Street from 1976 - 79
re "I have recollections of some GWR collett tenders, i seem to think they were from Castle classes (50xx) and my dad had the numbers, but i might have underlined them as mk1 TSOs in my book !!"
You are correct - they were still there when I visited Swindon in April 1981. They were numbered '1' and '2' and were being used as sludge carriers. I too would like to know what happened to them...