That machine doesn't look bad at all. With some clean up work, it ought to be ok.

Any time I come across something like that, I always unplug all the connectors, remove the two (sometimes three) bolts that hold the bottom panel, and lift out the bottom panel. Sure makes servicing the relays, steppers, and score motor easy. Plus it save your back from all the stooping over. Makes it easier to clean/sanitize the inside of the cabinet too.

The inside looks a lot like a Playmatic machine judging by the various assemblies and relay coils.

One thing you'll likely find is a bunch of bad (falling apart) light sockets throughout the machine (mostly on the playfield). Also, many of the playfield switch stacks are riveted and fall apart. When that happens, I unsolder the particular switch and take it over to the vise. Then with a proper size of pin punch, I punch out the rivets (or drill out if stubborn). Then I take the baseplate the switch was riveted to and with a 6-32 tap, I tap the holes to thread then to 6-32 machine screws. I use screws and sometimes nuts to reattach the switch to the baseplate.