I want to wish you well with your project. I am just finishing a 2.5 year frame off restoration of a 1949 Desoto Convertible. In the process I learned a couple of things that I would recommend you keep in mind.
1. Clips. The low production convertibles from MOPAR used clips not generally used on the other cars. No one makes them and NOS are almost impossible to get. So, take your time removing the molding and SAVE your clips at all cost.
2. Dash, inside door hardware, and a few other places use NUMBER 12 AND NUMBER 14 screws. The dash was a bitch as this became a problem. They used number 14 screws in the dash to hold it to the body. 1/4 inch is not a number 14 screw. I had to hit a bone yard 4 hours north of San Francisco and spend a day pulling enough good screws. Even if yours are rusted, soak them, heat them, but get them off clean if you can.
3. Door seals. The top end of the door seals were a molded special end. I cut mine off carefully and came up with a process to rejuvenate them. Hunt me down if this is the case on this car and I will talk with you about the process.
4. Pads. In my case a lot of the body pads are not available. I don't know about '53 and Plymouth. My suggestions is to make sure that you take any die cast off carefully and try to preserve the pads as you may have to rejuvenate them or use them for patterns.
5. Engine and Trans. We found out the hard way that at least on the 1949 Desoto's they bolted the body hard to the frame. No body pads. I confirmed this with several other cars. The issue was when we tried to put the engine in. The engine and trans will not go in as a unit on this particular body. The trans bell will not clear the frame-tunnel from the front. This, at least for 1949 Desoto, is a convertible only thing. The trans has to come out from the back. We think they bolted the body hard to the frame so the doors would close better and for scuttle shake. So, do check and see if the engine and trans can come out as a unit or you have to take the trans out first. We took the body off and then the engine-trans. We hade so much fun going the other way!
I am sure there are other items that are buried in the back of my head. If you want to chat them send me a PM and I will send you a number. Good luck and do pay attention to the advise of others. You will spend more than the car is worth to get it restored than if you just went out and purchased one done.
Good luck again on your project.
James