theyve pretty much got the same purpose of roller rockers.
they sit right under the cam shafts, its the first thing you'll see once theyre off.
it shouldnt be too expensive to fix, i got away with replacing my lifters that were stuffed without undoing the timing belt tensioner. each lifter cost me $75 each with the SAU discount from nissan, retail is around the $118 mark, someone said that UAS in sydney sell them for $45 each.