yes there are nuts on the backside, you'll have to remove the interior quarter panels and possibly pull the headliner back to get to some of them and the rest can be accessed from the trunk. they are nearly impossible to find, at least for the 69's, though the 67-68 may be repro'd not really sure. i broke mine thinking they had clips back when i first the car in 1984, didn't have any on the car until just a couple years ago.
Well, they are easy to find for 65-68 (didn't look for 69+) But more than likely I'm converting to painted hardtop...vinyl roof just doesn't do it for me. though if I saw a sharp one I might be persuaded.