I recently purchased a copy of "Diesel Dawn" number 6 "Brush Type 2s, D5500-5699, D5800 D5862, By Gavin Glenister.
And on page 56 there is a photograph of D5835 in Green with SYP, which had a engine rated at 2000HP as it has a different configuration of grills fitted to allow more fresh air into the engine compartment. The photograph says it was taken in York while the locomotive was undergoing static testing in April 1962. ( I was Born that year).
I also have "Looking Back at Class 31 Locomotive" by "Kevin Derrick" which is another great reference book to have in one's library. On page 72 there is a photography of D5553 in green with SYP, but fitted with " experimental flashing lights". The photograph was taken 1967 but it dose not say where it was taken.
I have posted the photographs as I did not want to get in trouble.
Terry.