Steve,
My 1963 Crown Imperial has seat belts for the front seats. I don't know
if it has them for the rear or not. If so, they are under the seat.
I can give you the part number off them if it would be of help.
The "buckle" I guess you call it, is a simple chrome affair
with no model identification on it.
These may have been put on at a later date. I don't know. I do know they
say MOPAR on them.
I can also measure under the car for the mounting points, if you
like.
Danno
I must say that I feel a little like I'm walking around with no pants on
without seat belts. JC Whitney sells belts that are visually
similar to those found in the "lesser" cars. I remember
reading somewhere (sales literature?) that there are mounting points in
the car (a '63) for belts. I even considered installing the
shoulder belt sets from the NYB, but that would require an anchor point
on the roof.