The lifters are not in the heads. To see them you must remove the intake manifold. Also, if they were making zero noise in the past, thay are most likely hydraulic. Soilds always make some noise. This site will help you determine if it's a real 289/271 or just a plain jane 289 4bbl with a HiPo air cleaner: http://www.hipomustang.com/images/hipoeng/

 

K-Codes need to have the valve train adjusted about every 10,000 miles....I have a beat up old valve cover with a strip of metal cut out so I can adjust the valve train for my 428

 

Don't the heads also have "289" written on the top of the head between two of the rocker studs?