I've added the inner band of steel to all of the smokers I've built, and never had a problem, including several made out of stainless steel. I use 1/8 X 1-1/4 flat stock, and bend it against my stomach, which coincidentally is about the same radius as a 55 gallon drum. Leave it a little long ( A 6' piece will be a couple inches too long) wrestle it in to place, and put a lot of clamps on it to even it out. If you don't have a lot of clamps. start at one end, and start drilling holes every 5" or so. Keep bolting it in place as you work your way around. Once it's nearly all bolted in, mark the overlap so you know where to cut. I always cut mine a hair long, rather than coming up short and having a gap. If you're going to weld it in instead, you'll have to get the length right before you start welding, but at least you could fill the gap if there is one.
Another option for a tall lid is to cut 1/3 of another drum to make a lid. Cut it at the top of one of the ridges, so it will fit over the top bead. This makes a big, but heavy lid. The 2" bung hole is cool for a chimney stack made from pipe threaded in. The 1st pic is of the flat band installed on my SS drum; the second pic shows the lid made from 1/3 of a drum. BTW- My drum ran hot without an exhaust stack- I think from wind blowing into the bung hole.