The caps you are missing, are they the snap on metal caps that fit the end of the axle shaft? As for the stack, it's a straight stack, and Nylint or Tonka parts might fit. Some of the Tonka Toys had straight stacks, and I think Nylint did as well. This was the biggest of the Doepke stamp steel toys, a big, heavy monster at about 14 pounds and almost 2 1/2 feet long. I'm not certain, I think that the red paint was International harvester red or Farm-All red. I think, not certain. Be careful when you start to take it apart. Stamped steel is sort of forgiving when you bend it, I would recommend heating the metal before you try and bend it back into shape or to bend any of the assembly tabs for dis-assembly. Work slowly on the bends, a little at a time. Heat the metal with a heat gun, not a torch, and just enough to help it bend without cracking or snapping the tabs off. Too much heat will distort the metal and cause it to warp. Use a metal stripper, a gel type furniture stripper will do the job. Brush it on and let it set for about 15 to 30 minutes and then have at it with a wire brush. Several coats of stripper will need to be applied to get all the paint off, and then a light sanding before you prime it. I would use a white bare metal primer instead of gray. Red is a very thin pigment color and will change color over gray or black primers. For the truest color I use white primer. Light coats of primer with sanding between each coat to fill in any low spots or pitting from the rust will give you the best finish.