You need the door flange kit. I ran into a snag when I went to hook up the gas line. On the old tank it attaches to the back upper left. On the new tank its on the front lower left. There was a gap on the plywood support for the hot water tank on the left side. I was able ti move the gas line through the the gap and with some minor bends I was able to get the gas line attached. It was't easy but I got it on.
We got a 4 gal unit and place it under the sink in the original spot Earlton Boler works used. new hole is bigger glad we save the cutout used it the repair around the furnace hole as the old one was vert and the new one is horizontal was close fit though.