These should be the trucks that are on the car. I found them on Lionel’s parts site and they are listed as an offset mount. I’m guessing looking at the car this was done to get a more solid mounting spot. The car must be disassembled to access the truck mount screws. Similar to an MTH.
It looks like the side frames are staked on. Not sure if you can install 2 rail axles. If you can get the trucks removed. You could cobble up a small bracket and make up an offset. With the Atlas trucks. I’m guessing you have the diecast ones. The car may sit to high. The Weaver trucks might work out better if you try doing a a offset bracket.
I’ve modified both Atlas and Lionel trucks using just the side frames for some 2 rail brass to 3 rail conversions. I did a couple of milk container on flat cars where I used a Lionel truck. The Lionel truck is a longer wheelbase than the prototype. In order to get it under the car better and avoid some details. I created an offset mount. Similar to what you need to create. I’ve done this with the Atlas trucks to. Just use the center piece as a template on some brass or aluminum stock to get the spacing right.
Once you get the car apart. You can what you need to get trucks under it. If you can mock up something that looks like it might work. Get out your height gauge and see where you are as far as mounting a Kadee and what you can attach it to.