Here's what I know about the bike:
The Shogun 500 I have is almost certaily from the early 1980s based on the full Shimano Deore triple touring drivetrain (downtube shifters, front derailleur and rear derailleur).
Deore - Originally an early '80's touring group, designed so that almost all adjustments could be made with a single 6 mm Allen wrench. Evolved into Deore XT MTB group, DX and LX spun off later.
(From Sheldon Brown's Website)
The Bike is made of Tange Champion #5 tubing, which I've recently found out is straight-gauge chromoly tubing with an estimated weight of 5.5 lbs for a built frameset. So solid stuff, but definitely not lightweight or high-end. But maybe the heavier gauge tubing was meant to match the touring geometry and rack/fender brazeons? Or just to put it at a lower price-point?
Tange #5 tubesets used 0.9 mm main tubes, 0.8mm seat & chain stays and 1.0mm fork blades, Advertised weight was 2460g (5.5 lbs) for a built frameset. Hopefully this is enough to allow comparison with Tange 1-4.
It's got Shimano Tourney AID cranks and Tourney long or medium reach brake calipers. The wheels are 27", have 36 spokes, and use the wider 1.25" tire size.
Everything attached to the bike was Japanese-made, almost entirely Shimano. I have changed the original handlebars for a wider set (originals were only 39cm) and put a longer stem on the bike (original was a shockingly short 60 mm). Everything else is stock and runs smoothly.