Quit fooling around and get a SA XL drum brake in the front hub. Mine has 32,000 miles and now on it's 3rd bike. Stops exactly as well as my new one.
ZERO chance it ever got more than warm.
The OP setup has a 99% chance of failing on the first hill at 35 mph. LOL What trash. The stays look like twigs.
The whole idea of a drag brake is a 3rd brake. So that excludes the other silly attempt with the removed canti.
Anyway, a disc brake is great for stopping but a POOR drag brake. It'll fry in no time. OTOH My Rohloff DIY disc mount is 100% successful.

Before it I had a 98% useless caliper for 13.500 miles. So I crossed Vietnam, 900 miles in China and across BC to Seattle where I got it welded.
I had ZERO problems stopping or slowing the 290 lbs with ONLY my SA XL-FDD in the middle of clay hills or 10 mile hill etc.
Actually I dangerously went down a 7 block STEEP hill in N. Vanc. I had to nibble down 3 feet at a time on the sidewalk. It would have been a struggle even getting off the bike. Before that I only barely pushed my bike up another steep hill in the east side.
>> Anybody saying SA drum brakes aren't good must of had the small size or an antique like shown post #17. My CCM has the small hub. The big one would look silly in a 650B rim.
The long brace arm Rohloff is 10 times better too. It saved me in a couple crashes actually.
This is a tandem fork from R+E, they raked it to 66 mm and added 6 mm brazeons. I changed it from 53.5 trail to 61. Handles beautifully now.