I've successfully sandblasted sheetmetal on older vehicles. That included my 29 Ford Tudor. What warps the metal is having the pressure too high, and staying in one spot too long and heating up the metal, allowing the pressure and heat to warp it. You feather blast a small area and go elsewhere, come back to that area later. The curves on those old fenders, aprons, etc. are hard to warp, but if you are not careful you can. The frame, rims, etc. blast away. So, it can be done, take your time, and don't rush it.
Rick
