Plankbender, this thread has bent out a bit from your original question and the answer lies in CAR41 (1)
The holder of the certificate of registration for a class B aircraft must
ensure that all maintenance required to be carried out on the aircraft
(including any aircraft components from time to time included in or
fitted to the aircraft) by the aircraft’s maintenance schedule is carried
out when required by that schedule.
Also read CAR 42 A, B, C and D along with Log Book Statement to find out which system you are using for maintenance and if it is CASA Schedule 5 note that it includes all categories airframe, engine, electrical, instrument and radio. Your MR stated in an earlier thread that it was marked on the Part 1 , CASA and Piper schedules, if so it would mean that you most likely have a CASA approved system under CAR42C as CAR 42D talks about, in which case AD-ENG-4 does NOT apply as it states clearly in applicability that it only covers 42B.
If want your LAME to swap the system under 42B and AD-ENG-4 giving you the freedom to carry out 50 hour oil and filter changes all the other prerequisites detailed in the AD will have to be complied with.
Finaly I really dont want to continue this topic as there is only one set of rules that apply to this thread and its digressions, it is only a few pages long, simple to understand and it is the LAW (note CAR41 (3) An offence against subregulation (1) or (2) is an offence of strict liability. Note For strict liability, see section 6.1 of the Criminal Code. You dont need four LAMEs or a forum to interpret their undersandings of it as there is only one set of simple answers under Part 4 Maintenance and if you have any difficulties you should approach your nearest CASA office to clarify it.