Hello Stuart,
Many thanks for sharing this, fantastic find and very lucky to have it in your collection, I have somewhere( must look harder) a parts label from the IAC dated 1959 and refers to a part from Spitfire 159, which I believe was one of the 2 seater trainers they had..wondered if it was still flying?
Spent today sorting through original spitfire parts including some still boxed with the 26AJ part number and 300 part number on the boxes, have a feeling that Mr Adlam will be after your label for his site 😀
Regards
Jason