Thxs. It's interesting that bars are SR. At the time, the Japanese component companies were divided into two rival trade associations, JEX and JBM. SR was part of JBM, while the SunTour derailleurs, Sugino crankset and original Dia-Compe centre-pull brakes were part of the JEX group. It was very rare to mix parts from competing trade associations, so I wonder if the bars (and stem) may also have been changed? SR bars typically have a date stamped at the end, but you'd have to remove the tape. However, if the stem is also SR, you could check its date code, which is typically stamped just below the insertion mark. The bars and stem may have been changed by the original owner, to achieve a better fit.

Regarding the saddle, the presence of a Brooks almost certainly indicates a post factory replacement. The original owner probably rode a Brooks Professional saddle prior to the Nishiki and changed it as personal preference.