I have never seen brakes like that. The pads look ok. 1/4" thick should be a good thickness. I would check the cam that squeezes the brake pads together. It might be worn. Does the lever go forward further or is it stopped by the plywood? The plate with two 1/4" bolts doesn't look original to me but I could be wrong.
There are a few posters that will know what that is. If they don't respond in a few days, you might consider top posting so they see the pics.
Good luck with it.