For best underside acces you can tilt the playfield out of the hooks and swivel 180 degree and lay it upset down in the cabinet.
Maybe put a towel between the apron and lockbar receiver. This was a practice of the 80's when games were operational, not sure if it is still applicable for collector games like Fathom. Best done with two people on first try.
I have a pic of my ebd, it does not have the exact same playfield hooks but at least you see what i mean.

IMG-20170724-WA0000 (resized).jpg

Edit, i see you have the rubber grommet missing on your right side pivot. Maybe inspect if it is important for an inverted playfield to rest on before attempt.