Removing engine compartment sound absorber?, Tips? Tricks? Gotchas? Options

[BillC]

What's the best way to remove the engine compartment sound absorber in a '73 914? I'm talking about the sound insulation sheet/panel attached to the firewall in the engine compartment. Mine is in very nice shape, and I'd like to re-install it when I get done cleaning up the engine bay.

There are 3 or 4 large plastic "washers" that are holding the center area of the insulation. Any trick to getting them off? I can't figure out how to do it without breaking them. I tried turning, pulling and turning-and-pulling, but they won't come off.

Also, is 914-559-377-10 the correct part number for those plastic fasteners? Porsche calls them "plastic plug", but the pictures online don't match what I see in the car. The pictures look like a large plastic "Christmas tree" that gets pushed into a hole. But, the parts on the car look like they fit over studs welded to the firewall (i.e., the plastic fasteners on the car look like they are female, but the pictures show male). One of mine is broken, and the others should probably be replaced anyway once removed.