I too, am curious about the fork.
A thick welding bead run up the backside of the fork leg from the dropout to several inches above the upper caliper post mount would do a lot & be subtle when doing so. It also wouldn't be a big deal to get a prefab mount from Paragon or Framebuilder Supply then fashion a reaction arm out of ¼ inch plate steel to spread the load half way up & then limit it to a 160mm rotor or whatever to keep the brake torque at a sensible level.
Something similar to this:
Disc tab with reaction arm by
Richard Mozzarella, on Flickr
The video really offers no clear shot of the front brake tab & in fact I'd venture a guess all the camera angles are suspiciously chosen to obscure the front brake work all together.
You can do a lot with old steel. I have an all Ultegra 6800, modern 1&⅛ straight steerer carbon fork with extended rear dropouts & relocated stay braces & canti brakes on a '74 Schwinn Varsity. A lathe, a welder, some time with a brazing torch...It's just time, really.
20190105_133655 by
Richard Mozzarella, on Flickr