Yeah, a drum has two heads. They're held on by rolling the metal of the head over the metal of the drum. To get them off, grind through the outside layer all the way around, being careful not to damage the end of the barrel metal under the head. Imagine that new type of can opener that runs around the outside of the can lid, so the lid lifts right off. Same principle, except this can edge CAN cut you! After the head is off, grind down the sharp edge left on the drum and on the head. Hit it with the wire wheel too. Now, if you were really lucky, and found a drum that fits the kettle lid perfectly, you don't want to grind on the outside of the seam to take off the head, or it'll end up too small. Cut around the inside of the lid with the sabre saw, and clean up the rough edge with the grinder and wire wheel.
The
Weber kettle lid has to fit snugly on the drum. If the drum is too big after
removing the head, grind the side of the top seam evenly all the way around. Go
a little at a time, until it fits.
The fire ring keeps the coals from touching the sides of the kettle, and helps airflow to the top of the fire. Most anything will work, as long as it's not galvanized or aluminum. I used a section of old water heater tank, 16" in diameter and three inches long. The rest of the water heater helps with the next step.
To seal the bottom, and keep the drum from sliding off the kettle, you'll need to make a flange. Cut two pieces of 1/8 x 3/4 flat bar long enough to go around the bottom seam of the drum, about six feet. Bend the bar in a circle. You might try wrapping it around an old water heater tank. Clamp the flat bar to the bottom seam of the drum, so that about 1/2" extends below the bottom edge of the seam. Tack weld it in place, them move the clamps and weld, move and weld, working it around the drum. Cut off any excess bar. Repeat this process on the inside edge of the drum with the 1/4" square bar, then the other piece of 1/8 x 3/4. Try it out: the flange should fit right over the lip of the kettle bottom.
Mark a line around the lower part of the second drum at the height you want the base of the kettle (14" to 16" works for me) and cut it off. This cut must be straight and square, so the thing will sit level. Lay out three 8" x 12" rectangular openings spaced evenly around the base, and cut them out. You want the pieces nice, as they are going to be doors. Clean up the edges of the holes and the pieces with grinder and wire wheel. Set the kettle in the base. Mark two slots where the kettle handle will go, and cut them out. This allows the kettle to sit down in the base without having to cut off the handle.