Those holes normally get wood screws, my guess is that a previous owner over-tightened and stripped the holes, then drilled through the playfield to fix his mistake.

BTW I'm in the midst of an Earthshaker shop right now too, and one thing that really bugged me was all those deformed black plastic spacers everywhere. I bought a bunch of similar ones from Marco with a narrower hole for the bolt, less likely to deform that way. They're 2 7/16" long so you'll have to cut them to fit, but each should yield two shorter ones.

http://www.marcospecialties.com/control/keywordsearch;jsessionid=C25B10A972F8863B0C08D45E7D2E4DB8.jvm1?SEARCH_STRING=254-5035-00

Yes, they're part of the playfield, but originally (on my playfield at least) they were for a wood screw post that screwed into the pf, versus a machine screw post that went all the way thru the pf into a t-nut underneath. Someone likely drilled the hole the rest of the way thru the pf, I had to do this for a couple of posts on a Sorcerer where the wood screw post hole was too chewed up to stay tight, and a t-nut and machine screw post were necessary.

I got ten, yields 20 posts which I'm sure is more than enough.