I got the bike home, thankfully the tires, bad as they looked, were reasonably fresh, and were able to hold pressure. The metal recycling plant had a few thousand bikes, compressed onto pallets, to be shipped to China to be made into who knows what. Thankfully, some who works there who pulls out any bike he thinks might be of value, and attempts to sell it online.
A Tange Levin headset, pretty common for good Japanese bikes,
Serial number is OSR 33, there are no other numbers on the bike.
The frame and fork both have Suntour Superbe Pro dropouts,

Beautifully made fork,
The same lugs can be seen in the 3 Rensho catalog on the Cyclone Standard model bike, the Super got different lugs.
Seat stays are unadorned. Thankfully none of the hardware was frozen, and I was able to raise up the seat. There is no paint inside the tubes, so it looks like it was originally chrome.
The bike rides well, the index shifting is new to me, but works well. The brakes worked surprisingly well, but the bar tape is dry rotten, and got white powder on my gloves, fingers, and on some of my clothes.
I don't think the 600 Biopace driveline looks very well on this bike, though I have to admit, it works very well. The rear wheel was upgraded at some point, my first thought was that the shop put on one of the many wheels that were sitting around, except that both wheels have matching tubular tires.
If it's not a 3 Rensho, whatever it may be, it seems to be at least as good.
An added bonus was while I was passing through the neighborhood, I saw a 1970 Dodge Charger sitting behind one of the shops with a lot of other old and unique cars. You don't often see such cars in Japan. I formerly owned a '70 Charger R/T, back when you could get one for cheap. I'll have to ride back out and have another look at that car.