Hola
The sales booklet for 63 has the belts listed as a dealer installed item. If
you should remove the head-liner you will not find a hard spot for a shoulder
hook up. When you remove the rear seat you will be able to install a set of
rear belts at any location that you want to drill a hole.
My front seat belts where in the car when we got it. The rear seat belts are
from a 67 Chrysler 300. Both belts appear to be of the same design.
Rodger & Gabby
47 De Soto Custom
63 Le Baron
66 Le Baron