I made several years ago. I just put a flat plate toward the top of a wood stove. I used copper tubing shaped to drip the oil in the middle of the plate. I controlled the flow with just a common gate valve. I just had a smaller tank that would gravity flow the system.
It was more of a supplement heat than a main source type. You usually had to have the stove good and hot with wood then turn the oil drip on. If you did not have it good and hot it would just smoke a lot an not put out much heat. Used oil will not burn that well straight. It is more of a smoldering type of fire.