Mystery 80s Japanese touring bike?

I acquired this mystery bike from FB Marketplace (local listing), because I could see the potential in this "diamond in the rough." Lugged steel, canti posts, what appeared to be decent components; for $20, I can't really go wrong. Had to look past the horrible rattle-can paint job and general parts disarray, no big deal.

As near as I can tell, before I start removing paint, it seems I have an 80s Japanese touring bike, of fairly decent quality. Here's what I know so far:

Serial #: J810057 (The frame is 57cm x 57cm, so that makes sense; made in '81, possibly? And the "J" I'm not sure of.) Any idea about this format, T-Mar?
SR triple crankset
SR Randonneur bars
SR Royal stem
Dia-Compe levers (no brakes, but likely were Dia-Compe cantilever, based on remaining hardware)
Sunshine hubs
Araya 27" alloy rims
Shimano rear derailleur (not familiar with model, haven't looked at number yet; I'm guessing not original stock)
Suntour BL front derailleur (broken, but could be fixed)
Suntour downtube shifters
KKT pedals (probably not original stock)
Lugged crown fork and nice looking scalloped seat stays and lugs
Original color appears to have been blue
Headset and BB bear further exploration

This will be my first real grounds-up refurbishing bike project, beginning with the paint issue. Should be fun.



More pics...