Not IMHO unusual to find those painted black after all these years. And though there is the possibility that the sub contractor that supplied San Jose (typically painted black top and bottom) common thought has been that NJ and Dearborn cars were supplied by a second supplier that provided them in P&O
For another unrestored example built prior at Dearborn to the example you found
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Looking closely (difficult due to the glare and angle of the sun in the shot) you can make out a difference in the finish between the shock tower and shock tower support arm and the shock cap