What year Tim.
They are very different, especially at the rear. The 63 has more a rounded sloped downward at the rear and is straight across on the lip, whereas the 64 has a sharper edge and contoured in the center to fit around the license guard bezel.
Here is a visual showing the 63 (Top) and 64 (bottom) and how they contrast:
And of course with the 63's you also have the shorter trunk lid used on the 1963 Sedan de Ville Park Avenue short deck body style.
The 64 has the camel hump in the middle of the trunk lip for the license plate. the 63 has no hump.
If Russ or no one else has one email me at firstname.lastname@example.org with your contact info and I can put you on my Wait List.
I've got two excellent condition 64' deck lids Tim