Yeah, I'm bagging the whole idea. Had I planned on using it that way with some sort of drain valve in place, it would have made more sense. No worries. Now I know.
I do the smoke damper on the stove the same as the cap on the top stack...
3/16" flat bar, 5/8" nut.
5/8" all thread welded to the hub cap.
I completely lucked out on how the hubcap flange meets the flange on the stove.
I ended up fubaring the Olds logo, but I didn't really care about that in the first place. I just thought the shape might work from studying the seller's pics on ebay. I have since peeled the chrome outer trim completely off the inner hubcap. It's getting painted high heat black anyway, so not a big deal.
Dampers all sorted, so I turn my attention to the doors. I bend a piece of 1 1/2" x 3/16" flat bar by hand to match the tank radius. Once satisfied with the shape, I weld it in place. This seals up the gap between the doors.
I will still trim the outside edges of each door. After that, plugging the existing threaded holes, and installing the thermometer(s), it will be time for another test burn or two. Maybe next week if all goes well...