there was one of these in a thread about 5 years ago (IIRC) and I think it was even the same color paint but that one only had the very distinctive headbadge and no decals...so yours is a step ahead! If you try a deep search you may be able to find that old thread.
Obviously a pretty high quality Japanese production frame and yours has some pricey components, too, some of which may be later upgrades. I never have seen one of those Belt seatposts that copy the early Simplex! I think it may be slightly earlier than '80s and interesting that it has the 'diamond-pierced' lugs that Miyata used on some of their better frames (and used on some Univegas they built) which may be a clue as to the builder...but may not.