I was JUST looking at those on Amazon. One of the companies sells a stainless version that I'm going to get to make it easier to get into the back door. I'd love to have some RV type pull out steps, but those are seriously pricey!
We have them on the front of the bus and they are great for getting up to the engine compartment.
My '46 came with one that looks just the same and was used to reach the windshield on the driver side. It is installed with bolts going through the body and a small piece of 1/8" plate steel on the back side. Appears to be original, so they can definitely be mounted securely. I am adding another one to the passenger side.
PS...if you plan on welding it and it is galvanized...be sure to thoroughly grind away the galvanizing along the areas you want to weld.
My 00 Amtran has these mounted like Tango's. Just behind the front tire on both sides to help you get up to the windshield to wash it, or to get better access to the engine when the hood is up... They're pretty useful.