You could make a drop bolt (drop bracket) and use normal reach brakes.

Don't mess with trying to get super long reach brakes to work. They might sort of work in a perfect situation, but what about when you're descending a steep slope, in the rain, rims slick with muddy water, pads worn, 250# of rider and gear.

See Sheldon Brown's site on drop bolt / bracket. Or search here.

But what I'd really do, if you want 26" wheels, is use an older hardtail MTB. Frame will be made for 26" wheels, lots of clearance, eyelets for fenders and racks, cantilever brakes, high bottom bracket. Very strong, something to consider for your load. Will already come with the gearing you'll want. Do a drop bar conversion.