The '63 Buick hardtop has an Advanced Custom front pan with a '61-'62 Chrysler grille, and I believe the regular custom includes a '56 Buick grille bar. A couple of annual kits used cut-down '60 Mercury grilles. Mostly it's wheel covers: '63 Mercury hardtop kits had '50 Mercury caps while the convertible (and both '64 kits) used the Cadillac covers that were better than what Jo-Han put in the Cadillac kit.
Some are fudged to the point of not being recognizable, like the cut-down '62 Dodge grille in the '63 Corvette annuals. For the '63 annual kits, look for the four-page color ad spread in some period magazines; that lists the features in those kits in detail.
Another neat kit is the '32 Ford sedan from the double kit. I believe the wheels are described as Continental Mark II wheel covers, and I'm pretty sure the steering wheel is a second-gen Kaiser piece. Lots of neat stuff, once you find out what the parts actually are--
--Mark