Not a question anyone asked, but FYI if interested:
I believe you'll find the fork was made by Tange. Drop it out f the frame to see the stamping on the steerer, if you want to know. "Tange" stamped there means they made the fork, not referring to the steerer — they didn't stamp the steerers that other makers can buy for building their own forks. You can even see the Tange stamp on some Trek forks with Reynolds 531 tubes, Tange would build with whatever the customer ordered.

Those rear triangles look to be Tange-built also, but there's no simple way to prove it, like with the fork.

Nothing wrong with that; Tange made high-quality forks and rears. In the '80s, Davidson used Tange forks and rears on the less-expensive production bikes like Impulse and Discovery, with just the custom bikes having them made in-house. Though later (about 1990) the fork making was brought in-house for all models. Bill D visited Tange's Cr-Mo fork making department and was impressed that they just had a row of single fork brazing stations, each with one guy brazing one fork at a time. Not a "production line".