disassembling post war cars

 Listing the exact car numbers for any "problems" would help, but in general...

 My "lobster claw coupler" cast post war has a plate single screwed to the bottom frame that holds the truck. or its "inside" on the frame. Most trucks have a post, and horseshoe clip/ C-clip/E clip holds it. Some are riveted on the body, or plate. Some are held by machine screws/nuts. Some have thrust washers, a couple have spring washers.

  The key to truck swaps is leaving just the right the right amount of "slop" to handle grade changes and sloppy track without body friction, but not have the cars leaning too hard.

 Bodies either have a screw in each corner on the underside, or one on the end, above the coupler. I remember one caboose as a kid that the body was held on by turning the stack, and doing something to the ladders, but I cant remember who made it right now.

 Unless the old bodies are useless for even a repaint, Id take a look at new trucks too. They roll so much nicer you can pull more cars easy, and the all metal trucks, still have "the heavy feel". Hey the caps even turn 

  Come to think of it, putting a set on cast post war would make them actually roll nice, and the weight would be useful to stop curve string lining of the forward section on long trains.

 You might want to add a coupler to the caboose where its missing one too.

The metal red caboose is likely a 2457 which you have to unbend the body tabs at the frame and ends to remove the body and have access to the trucks.

 I assume the gondola is the longer version in which you need to bend the four metal tabs on the frame under the body to release the catch and remove the body.