Interesting. That s/n format is different than others I've seen for SR frames, typically Miki, Araya or an unknown builder, s/n (LLNNNN). That could explain the difference of the FD hanger on yours.

Based on @T-Mar's Asian Serial Number Guide, that format follows the S(2) format (SyFxxxx) associated with Shogun, and implies a mid-1979 build date. That would predate the other Dura-Ace SR bikes I've found, which were nominally 1981 models.

More questions for you: What size is the frame? What generation DA components were on the bike? What brand is the rear dropout?