i fixed it like you tried,by making a longer pushrod.
changing the box oil wont fix it.
sounds like air in the line,you did bleed the air out of the system?
i used R33 n/a front rotors slotted & R32 gtst calipers for a nice front upgrade.
they work a treat and did the whole lot for $500aud.
but theyre still 4 stud.