On your seat, since you said your power seat finally arrived did you buy a track and base assy from someone and then are trying to make a formerly manual seat power? If that is the case I would wonder if the frame would have those brackets. Anyway, be interested to know what you find. Possibly the brackets were broken off if the welds are as weak as I consider them to be on the Caribbean frame.
In building the seats, and doing a mix and match I would have thought that as space constrained Packard was at Connor they would want to keep bulky pieces to a minimum so would have a stock of bare seat parts that were all the same. Some parts such as the base section of the frame might even be the same for sedan and HT seats. Even if they were done somewhere else where space was not an issue, for inventory simplicity reasons they might still start out the same. When an order came in for a car they would grab a bare bottom and a few small pieces, send them to upholstery where those with power would get brackets welded on, then sedan or HT back supports attached via bolts or welds, and that assy get bolted to the power tracks. Somewhere in the process upholstery and plastic end plates were added per trim code and that finished assy then sent to the line. A manual seat would not get the brackets and would just get the back along with the simple tracks and finish upholstery.
Another thing I was kind of curious about was it looked like Z springs are on the seat you received. I didn't realize they had started using Z springs instead of coils on anything but 56 Caribbeans with the reversible foam cushions. The coil springs were treated as a selling point in prior years on higher end models thru 50 I think because dealers could remove and change coils for stiffer or softer versions to provide ultimate customized customer comfort. Figured the customizing had probably ended with the early 50s because of all the penny pinching the board did with the 24th series but still thought regular cars used coils on the bottom cushion until the end. Maybe I learned something new.
Yes, adding power seats and this seat frame is out of, I believe, an Executive but the springs visible in the photo were from my own car and were original to it. I just laid the frame against it to check the fit. I can't speak for Caribbean as I've never owned one (but nearly bought a hardtop) so whatever you see in the photo is the way it came from the factory as far as springs are concerned. I stripped off the upholstery myself and it was definitely original!
Incidentally, I do need a nice pair of plastic bolsters in black should anyone be reading this and have a pair available.
