Your heads, if '65, should be fully adjustable...
The non-adjustable valvetrain applies to later heads that had a stepped stud where the nut bottomed out on a shoulder or bolt-in rockers where a bolt held a fulcrum into a slot in the rocker boss in the head....
Do your heads have a slot for the pushrod or a round hole?
Non-adjustable means that everything has to be right or else the valve lash is either too tight (valve doesn't close completely) or too loose (noisy)....
That often happens from shops sinking the valves when doing a valve job and not taking the same amount of the stem end...or, surfacing the heads more than .005-.010"...
Pat
http://www.jps.net/binay/webdocs/strtmstng002_sml.JPG