Really it was my first reaction too. Yours has steep angles, not a tourer. what is it ? A 60cm or so ? Checking the stay lengths against the Miyata etc. , you'll verify it's aggressive angles. 26.8 seat post diam., I don't think it's hitens, besides, old race geom. bikes weren't hitens for the most (very) part. It's no Miyata. Nishiki, I don't think so.
A whole bunch of brands that it most likely is not so I'll save it.
Panasonic, the very best and only one that could be considered had 4130, all Panasonics did tthat had chromoly so it makes little sense that they would have Tange dropouts and not advertise Tange tubing, possible, not likely as far as I suppose.
This is ALL deduction, how could it be anything else ? I checked threads here; the short version: Ser. #'s are all over the place. There was one or two fellows, owners that I spotted, submitted 4 or 5 digit #'s. The rest had a letter or two preceeding 4 numerals, the 0 could be an o..... whatever. Just shows that it or anything's possible.
Having seen a bike with embelished NON Japanese style, fancy lugs, I'll never forget. I saw two; one up close in real life and one on e-bay, both were orange, both were 1976 Centurions. The brand was all but unknown to me 'till 24 years ago, not big in NYC 'till that point in time, Cents. have eluded me. The ones I saw were only 2 and 3 years ago. BOTH had chrome lugs and that bussiness at the head tube, the curvatures etc.
Yours may've been painted over, maybe never painted. Cent. was much more well know for its hitens bikes prior to the '80s by most accounts. I'm no expert, I just remember things and am just as often wrong as right . Scrape a little for curiosity for chrome. Aside from the chrome lug feature, the Cents. including the one I was nosy with had paint on chrome. not all Co.s did that. Miyata as you know used an electrostaic coating under the primer coat(s) , under the base coat(s). Cent. and a couple(few) others used chrome, darn near show finish. It's all I got. Google it as 75, 76 to see at least one white one.