With the lock tight nuts get a small screwdriver and stick it into the nut hole from the underside of the playfield and then rotate the screwdriver with a spiral motion using a wide arc.

Since they are only held in with three spikes driven into the wood the lock tight nut will automatically loosen and detach itself from the playfield completely and then slide onto the shaft of the screwdriver.

Bit hard to explain but once you try it yourself it makes it very easy to do with 30-40 nuts.

And it beats trying to pry them out one at a time.