Drums to disk swap, small to big rotors ?'s

The calipers are the same between the 73 up A-body disk brake and the B-body. The only part necessary from the B-body besides the larger diameter rotors are the caliper brackets that bolt to the spindle.

Your 74 Duster should have the new style k member that has the sway bar that passes through it. If that is true then just mount the spindles so the calipers face the front in the stock location and use stock 73-76 disk brake hose. The only reason to swap sides with the spindles and mount the caliper to the rear is to make clearance for the 72 and earlier style sway bar. If you mount the caliper to the rear Aspen/Volare brake hoses need to be used.

NOTE: make sure the calipers are mounted so the bleeder is up or you will have trouble bleeding the brakes.