Vagrant02_DRFT

i have a low mileage engine in my 1986 s4(and i dont really want to swap a different motor in) , and from what i've read , the na s5's make more horsepower because of improved stock parts under the hood compared to the s4. now, im just wondering if the S5 parts that are better than the S4's , are interchangeable, can you swap out the older , obsolete parts for the better , improved S5 parts. any kind of info/help is appreciated. thx!