Plank, the first and only place you should look first to answer your question is your aircraft's logbook statement (LBS) Part 1.
This will indicate under what maintenance schedules the aircraft is bound by. The LBS should ideally be signed by the registered owner/operator as saying 'yep, I accept that'.
Further the AD/ENG/4 may not be applicable at all as it states that only if you are maintaining it IAW CASA schedules. Again, check the LBS first.
pcx has a good point, it also depends on how the 50 hrly is written up. Technically the Lyc SB mandates the filter to be opened up and inspected, which IS NOT covered under Schedule 8 - Pilot Maintenance - a small but important issue.
Do/get it done early and save the hassle!
