How easy is it replace rear brake drums with calipers?

first off what kind of car are you driving? most cars like mustangs and stuff you can buy rear disc conversion kits for under a grand. depends on your car, you cannot put front brakes on the rear because simply they are designed to have more braking force than the rear about 70/30 and you need more brake in the fron tif you put them on the rear it will screw up your brake bias rear drums and rotors are always smaller and lighter than front and most of the time arent vented. if i were you the best thing to do woul dbe rebiuld the drums and have them turned cheapest and most effective way to repair.