I'll happily give my two pennth

If the serial number is from 1986 it was presumably sold as a full bike.
The SBDU did framesets with SB numbers and Nottingham did full bikes with W numbers.
The over size seat stay caps were the hallmark of high end Raleighs so it's good quality.
Presumably the internal routing was done by Bob Jackson's when it was repainted.
I suspect the chroming might also have been done afterwards, 70's Raleighs had lots of chrome but I haven't seen many examples of mid/late 80's with chrome.
Not sure if the forks are original, have you got any better pictures?