..late to the party. And, all the answers are correct..
..but..
427's were shipped with all 4 dust caps in place. Factory stills and
PR material show the 4 wheels the same, all with dust covers.
...and the knock-offs weren't safety wired, either.
Rick's correct..the Comp guys may have let them 'fall off' in the rear, because they were cosmetic.
...so, pick your look...either is correct.