Color
Matt, the underside was not painted, it was only over-spray. Check this site out for factory markings, practices etc...Although mostly B/E body based, the same practices apply to A bodies.
http://www.mmcdetroit.com/Inspection/
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This other site is also one of my favorites for research
http://www.hamtramck-historical.com/dealerships/1971PlymouthDealershipDataBook-09.shtml
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All the best,
Giles
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