Brakes of any kind, disc, drum, or a combination of designs are there to convert the kinetic energy in the vehicle to heat and blow it away. As long as you've got good ventilation to the brake drums, those antique binders should do a pretty good job. I'd suggest fabricating some ductwork to pass a good volume of air across the brakes- - - - -maybe drill a few holes in the backing plates- - - -that's how we improved braking on the race cars back in the dark ages.
The 1934 Chevy truck/trailer rigs my family used to haul beer from Milwaukee and St. Louis to Nashville back in the late 1930's had vacuum over mechanical brakes on the tractors, and no brakes at all on the trailers. I think the gross weight of those rigs was somewhere around 4 tons- - - -vehicles plus cargo. They didn't wreck them- - - -at least not often!
Jerry
