They were gold CAD (Cadmium) plated originally, as were the same ones used on the VW 411/412.
PMB does excellent caliper restoration/rebuilds including new CAD plating gold or silver (they're a member vendor on here).
PS - there is no one best book, since they all seem to have some errors of facts in them.
Get several & recheck items on here & 914club, p914.com (& .net & .org) & at Jeff Bowlsby's website -
http://bowlsby.net/914/Classic/ PSS - 2 of the better ones at=re Paternie's & Johnson's but the latter is really a 356 guy who misses on some areas of facts, & Paternie does too - but they're still good resources.
B. Johnson's -
https://www.thriftbooks.com/w/the-914--9146...mp;idiq=2599991 P. Paternie's -
https://books.google.com/books?id=yMJFvrORt...p;q&f=false Both are around in older editions/cover art at reasonable prices, & not much changed in revisions - if anything.
Tom
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