It's been said fifteen times and I'll repeat it again for emphasis for some reason, that 428 was not factory installed. A dealer-installed option does not necessarily have the corporate imprimatur, some will and others won't. We do know in this case that these 428s did not. So while we know that there were Firebirds with 428s installed we continue to lack evidence of a "stock" 428.

What would be interesting to know is what engine those cars came with originally, it seems to indicate a regular 400 in the article, but could it have also been a Ram Air version?