There aren't screws on the ends of those plastics. They are rivets-- the center pops up, and releases the tension, you should then be able to lift the entire plasticassembly out, and the rivet remains in the plastic-- that will expose the light board. IIRC, you'll need the .39" rivet for this application, but double check that before you order.
Do be advised that some LEDs won't work in those boards-- I think it's a polarity issue.
Be gentle-- those plastics aren't available anywhere that I'm aware of.
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From the PBR website:
Gottlieb® Plastic Rivets NOS Gottlieb® Plastic rivets used on System 3 games.
GTB-MP10
GTB-MP91
