When disassembling my Dart to take it to the blast shop, I took the top part in the picture (that the heater hoses pass through) off of the firewall. When I got the car back from the blast shop, I found the part on the bottom in the picture laying on the passenger front floor pan. What I would like to know is, was there a second one of these pieces that went on the interior side of the firewall along with the one on the engine bay side? I thought there was only the one but if so, I can't imagine where the second one came from and I don't recall seeing anything stuck to the interior side of the firewall when I took the heater box out. Also, is the part that goes on the engine bay side of the firewall supposed to be painted body color or black? BTW, the second piece is metal.

I would think that the bare firewall was painted then later on down the (assembly) line the items including that support plate were added so I would assume it was black rather than firewall color. I did not think there was a seperate one on the inside either. Some one may have used it if they had an extra in their stash assuming that it was supposed to be in there. IF that is the case as you know no harm no foul but would not be OE. EDIT With more thought I'm thinking that I saw one of those plates on the inside on the heater box itself where the tubes exit out from it. (A body).

Only one of those rectangular plates was used on the engine side. It was black. All black pieces and brackets on my 69 Barracuda except the K frame and the rear axle housing were paint dipped. A film of gloss black enamel paint was poured on water in a vat, and the parts were dipped in the floating enamel. You can find runs in all these black dipped parts, such as the heavy bracket under the steering column and the parking light brackets.

The fastener holes on both pieces in the top photo look to be bigger than the screw O.D., so that screw would not be able to hold an interior plate. The screw hole in the firewall is the root diameter of the screw and clamps only a plate that's on the engine side.

Thanks to you both for answering my questions.

Robert is correct. The second one attaches to the heater box itself.