Can't quite tell, but your photo seems to show 3 large holes and 2 small holes. My 69 Barracuda has 3 large holes but only one small screw hole to mount the "plate assembly" inside the car. See the plate assembly at 69 Plymouth FSM, page 11-4, fig. 3, view E.

Maybe you are missing the R side exhaust hanger bracket that goes under the car and the plate assemply that goes inside the car with 3 bolts to fasten the bracket to the floor pan?

Here's a photo of my unmolested 69 Barracuda. I ordered the car in the fall of 1968.