I haven't had time yet to figure out if the posts are intended for cantilever- or centerpull brakes.
If they would be spaced for cantis with 700c wheels, I'm thinking whether they could be adapted to be used with centerpulls and 26" wheels? Unlikely, but theoretically possible, I suppose. Converting to a smaller wheelsize should also give more tire clearence, but I am aware of the potential pitfalls of going from 28" (622 mm) to 26" (559 mm).
Also I just realized I had written the brake post mount threading as M8 but it's actually M6! Luckily, after doing some reading online, I should be able to scavenge a pair of old RockShox suspension forks that surprisingly used to come with brake posts of that size