Fit is a vage term. The Aspen K member will fit in the 40 Plymouth IF you cut off your original frame at the firewall and build a 2" x 4" tube replacement frame to bolt the K member to. The torsion bars will be right up under the front nose/ bumper area, but should fit under the sheet metal. Of course, you will also need to fabricate a radiator and front sheet metal support and bumper mounting locations because those mounting locations will be gone with your original frame. A Dakota frame also fits under these cars, but with them, at least you don't have to build a frame to mount the suspension to. You still have to fab a radiator and front sheetmetal support and bumper mounts though.

So the answer to your original question about if it fits is sort of. Anything really does fit with a tourch and a welder, just some stuff requires more tourch and welder time. Gene