I've had a rusty/battered four-wheel Flyer 3013 sand car in the under-the-workbench parts box for years. Rather than "restore" it or gut it for parts, I've decided I want to make a stakeless flat car out of it...we'll call it a 301X. A pretty simple exercise, but I want to make a load for it as well, which will be a bit more complicated.
First step was to remove the body from the frame. Pretty easy, just straighten up eight tabs and lift it off. Unlike the Lionel 902, the brake-wheel and stanchion on the 3013 is attached to the body only and doesn't pass through the frame. I'll save the body in case I decide at some point to reassemble the car. I have a source for a replacement brake-wheel should I decide to do that.
Next step was to remove the the bits from the frame. Wheels, axles, and journals are easy enough. The wheels and axles come out with just a minor flex of the frame. I used the Dremel and a wire wheel to polish off the coating of rust and shine them up a bit, then set them aside. The journals are each attached with a pair of tabs...just bend the bottom one straight and they are easily removed. I have an old can of Brasso that I used to shine them up. That and a buffing wheel on the Dremel has them looking pretty smart.

The tab/slot couplers are a different matter. Both are missing their tabs, whether they broke off sometime in the last 90 years or someone purposely removed them, not sure (although I don't know why someone would purposely remove them). I couldn't find replacements (didn't try too hard, I'll admit). No worries, I'm feeling lazy and slot-only will work as long as the next car in the string still has its tab(s). The other thing is these are riveted in, so you'd have to drill them out and re-rivet them to get them back on. Initially I intended to repaint the frame, but the original paint is in nice shape with just a few scratches so I'm going to leave that be. I used the Dremel and wire-wheel to polish up the couplers in place as best as I could.
The last step in this initial phase was to drill one additional hole for possible use in mounting the load. Easy enough; once that was done, I polished the frame with a bit of Turtle Wax polishing compound, then a bit of Meguiar's cleaning wax. Once that was done, I reinstalled the journals, wheels, and axles.

I ordered a number of 3D-printed items from a printer I've used a number of times for other stuff; any one of them could serve as a load. Have to decide how intricate I want to make it given the prewar "tinplate" theme". More pics to follow.