My info may be out of date but If it is a lifter, then heavy oil will not help. Usually it is just a piece of debris in the lifter causing it to stick and when the valve stem hits it there is a clattering noise. Instead of using heavier oil , add a quart of transmission fluid in place of one qt. of oil . Run this for at least 100 miles and then change the oil again. Changing the lifters would probably cost more then the car is worth on the market although you might be able to do it yourself if mechanically inclined. Some lifters can be removed fairly easy with a retriver magnet. Others require disassembly of the engine. Your lifters are probably not adjustable as they are controlled by oil pressure.