Not familiar with the 65-66's, but the 67-68's do use stamped nuts. It would seen difficult to keep the trim in place by friction....
Hard part to replace as the headliner needs to be pulled back to access the nuts, and is tricky to get back in with no wrinkles... need to peel up the liner and look as you will need the same, or more, access to replace.... may end up needing to replace the headliner... be careful...