I got the cylinder off and below is the evidence together with pictures of the two secret weapons I used: one the antique offset wrench as recommended and the other a crow foot that I found worked very well to unscrew the flare nut at the upper end of the feed pipe.
Following advice I didn’t touch the feed pipe at its lower end where it attaches to the cylinder. To fit the pipe to the new cylinder I’m going to try to make a sort of 3-D template by, 1. setting the old cylinder and attached pipe on the bottom of a suitably sized cardboard box so that the free end of the pipe touches the wall of the box then 2. marking on the box the positions of the cylinder and the point where the pipe touches the box. So then if I assemble the pipe to the new cylinder so that they match up to the marks on the box I should be all set… (maybe)
Just as a footnote, it’s amazing how that offset wrench fits. When I first looked at it I thought, no way, but damned if it doesn’t just snake right in there and allow just enough swing to get the screw out!