If it's like my 72 demon there will also be a screw in each lower outside corner. When installing new pad be sure to find the holes for those screws BEFORE installing. They may be covered with foam from The manufacturing process.
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It's kinda like easter egg hunting, but with your finger tips.
Go slow, as I always say "working under the dash on these cars is like sticking your hand into a box of kitchen knives"
The nuts are in the corner of the back side of the dash metal where it turns down toward the face of the dash from the top of it.
Follow that corner with your fingers and you'll find them.
It would help to pull everything out of the dash (maybe you could get away with leaving the heater controls in, but the glove box & instrument cluster need to come out).
The screws at the ends are a real joy to get out...they're hex and the heads are really shallow (or at least they were on my '67), and a socket doesn't grip them very well. When I re-assembled it, I used phillips head sheet metal screws in their place.