I have several large vices on heavy tables. My largest one is a Wilton mounted on a table made out of 1" sheet steel about 4'x8'. We brought the whole thing into the shop many years ago with a forkllift. A vice has to be securely anchored to be of any use. Occasionally I need a vice at my house. I bought a Wilton receiver hitch vice. It is made in China, but its ok for around the house.
http://www.wiltontools.com/us/en/s/atv-all-terrain-vise/As for 16½x7 brake drums. They will will weld. We have all sorts of things made out of them. With scrap iron so cheap, we give them away. They weigh a little over 100lbs and have about a 17" footprint. That is stable enough for something like a grinder, but I'm not so sure about mounting a vice on one and expecting to do anything with the vice.
