Steve,
Howdy and welcome to the message board. I don't have a parts interchange manual but I don't think the Dodge trunk lid will fit your car. I could be wrong here but it has always been my understanding that, for the most part, only Chrysler parts will interchange with the DeSoto.... and that's not even a given. However, there were a few things that would interchange with Dodge, such as tailgates on the station wagons for example, so like I said I may be wrong and in your case I hope I am!
Hang tight and I am sure someone will come along shortly that can answer that for sure.
BTW, what town in NC are you from? I am from Charleston, SC. Quite a few members in our area of the Carolinas! If you haven't joined the Club itself, I highly recommend you do so.
Best of luck on your '48!
Dean Mullinax