Just my experience with this:
I wanted to buy the metal cover and found one at Vee Dub Service in Ogden, UT a few years ago. I tried to put it onto my engine bay and it would not fit. The edge where the plastic has about a 1" recessed space all the way around the margin of the lid, was different on the metal one. So, the metal one would not fit down into the hole and would not latch. The metal one had a "bulge" of metal where the plastic one has that margin of flat space that sits on the rubber seal at the edge of the bay hole.
 
bob
'87 Syncro Westy
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