XA903
2AV8,
Apologies that this response is over 2 months old but I was researching something when I came across your posting.
I worked on XA903 in both OLY593 and RB199 configurations during the 70's as an engineer at the R-R Flight Test Centre at Filton. However, I regret that I don't have any photographs of the cockpit - mores the pity!
I assume you have tried the Rolls-Royce Heritage Trust at Bristol and, in particular, Alan Baxter (assuming he still takes an active role in things - you'll have to excuse me but I'm a little bit out of touch with things at the RRHT) who was the Flight Test Engineer most associated with XA903.
If I can be of any assistance please send me a PM and I will do the best I can. Thankfully, I am still in-touch with some of those remaining from the halycon flight testing days at Filton.