The trim tag on the firewall will tell you the trim and paint codes. You can find the descriptions of the codes here:
http://www.teambuick.com/reference/years/63.php
http://www.teambuick.com/reference/y...rim_number.php
http://www.teambuick.com/reference/years/63/63paint.php
http://forums.aaca.org/topic/231704-...odes-by-model/
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