What kind of brake calipers on my ‘71 Duster 340?

Are the pistons seizing? If the pistons retract easily and apply without sticking, I would clean all moving surfaces with a file to get rust off and lube all sliding surfaces with a disc brake grease. This will not get hard later. Dielectric grease is one option. Check the pads for even wear. Use a sanding disc with 120 grit emery while lightly sanding the disc surfaces with the calipers off. Helps if a friend can turn the disc to evenly sand the rust off. Then bleed the brakes to get the moisture infused brake fluid out.
Any sign of the piston seizing is definately grounds to replace them. Those were a very common caliper used by Ma Mopar in the '70's.
At this time it is also probably wise considering it sat for a few years to replace the brake hoses front and rear just to be on the safe side. The cloth weave in the hose can deteriorate over time and they will fail. Any cracks in the outer rubber are a sign they need to be replaced.
Keep an eye on the rear axle seals as they may have deteriorated due to sitting. When they start leaking the rear brake shoes will get soaked. If it is just starting to leak, a good dousing with brake cleaner can deal with most of the oil and the rest will cook out. That is just a bit of oil on the edge. When they get soaked the shoes tend to grab and not release until you back up a bit.