Yes, you can just swap the manual regulators in the doors for the power ones. Just be careful when you drill out the rivets since the power arm is spring loaded. You can use bolts or new rivets to attach the manual regulars.
You will need new manual door panels and manual armrests, along with the manual regulators and window cranks. The power armrests are longer than manual ones and you can not use them with a window crank since the crank will hit the armrest.