Mine is a 73, but I believe the top edge would be similar...
There is a 'lip' formed in tail panel around inside edge of rear quarters, and that lip is also reflected in bottom part of trunk lid lower flat that seal mounts to...
Mine was painted up just over the lip, so I masked off body color edge when I touched up my tail panel...
Here is the pic showing tail panel/lip under quarter and over top of trunk lip...