Before getting too involved with ripping things apart try some automatic
tranny fluid or Marvel Mystery oil in with your normal oil (if you are 1/2
quart low add a 1/2 quart or if changing oil substitute 1 quart for a quart of
oil).  Have friends that sware by the stuff and it quiets down the lifter
noise by breaking up any deposits in the lifter.  Also remember that the
manual says "some lifter noise on start up and at highway speeds is normal" or
something like that (at least my 83.5 shop manual does).  Have fun.
Ken Wilford
John 3:16