There isn't a consolidated lists but you can find info here and there. - Fenders - 1963 & 1964 Cadillac Fender Differences is one showing the differences in the fenders. as a specific question and ther are members like myself that can usually tell you.
Here's a quick run down front to rear on large panels:
fenders - difference 63 to 64. There are also different versions for the Series 75 and commercial chassis for each year.
hood - core hood the same, althought 64 had hood extension moved to upper grill. and requires some drilling to mount the 63 hood extension to a 64 hood, and some cutting to make room for the hood latch.
doors - coupe & convertibles - have same coor door 63 to 64. (Of course glass and glass trim are very different due to shorter glass used on convertible)
doors - sedan front door - same 63 to 64
doors - sedan rear doors - different 63 to 64 due to higher ridge on the 63 for the taller tail fin line that starts at rear door. Also, 4 window Sedan doors are different from 6 window sedan doors within each year due to shape on inside rear of door. Fleetwood 60 Special rear doors are different from Series 62 and Sedan deVille doors due to power rear vent window in rear door.
doors, front and rear - 75 series (Limo), Commercial Chassis - different from all other body styles
trunk/deck lid - very different 63 to 64.