I’ve asked those most likely to know how the brakemen on the V&T cars did their thing, and the consensus seems to be that they walked over the ore loads and operated the brake wheels while standing on said loads.
This detail of a larger photo (Chollar mine, Virginia City) was pointed out to me. It shows 4 men, leaning against the brake wheels of 4 V&T ore cars. They may be mugging for the shot (which I’d assumed whenever I’ve seen this pic); but they may well be the brakemen running these cars into the Nevada Mill (behind the camera).
Notice that there’s no way to reach those wheels from the footboards. And since there’s no great way to climb up (there are no grab irons on the bins), if it were me hoisting my fat self topside, I’d want to stay up there until the job was done (and walk from car to car if need be).