The pictures are fine. Based on what I recall and my catalogs, I do not have a perfect match for your bicycle. The description, pictures, and date codes suggest that the most likely candidate is a Japanese manufactured SIU model.

The SIU was the new name given to the SHA around 1976-1977. It was the entry level model and matches your fork, derailleurs, shifters and crankset.

What does not match are the Tourney brakes and hubs. I recall the SHA coming with steel, center-pull brakes and steel, medium flange hubs. My catalog does not mention the brake model on the SIU, but specifies Tourney brakes on the SHC, so this seems to imply lesser brakes on the SIU. Similarly, the SHC hubs in the catalog are Tourney, but the SIU's appear to be a small or medium flange hub.

Despite the brakes and hubs, your bicycle is clearly not a SHB/SHC, as these came with 1/2 chromed forks, a cotterless crankset and Lark derailleurs with ratchet shifters.

There was no model between the SHA/SIU and SHB/SHC, so a SIU is the most likely candidate. The component discrepancies could be due to various reasons: changes in spec from one model year to the next; components substitutions due to shortages; owner upgrades or replacements.

The lack of tubing decals is not surprising. Even my top of the line SHX does not have a decal and it is Tange, double butted, chromium-molybdenum tubing! However, in your case the frame is hi-tensile steel. Sekine started using tubing decals on their top end models in the late 1970s.