Bill S: Nobody knows about Salford cathedral largely because it's the Catholic cathedral, which don't count. Actually Manchester became a (C of E) diocese just a year or two before Salford became a Catholic one- around 1850. Manchester town became a city in the 1850s, but Salford (which had the older town charter) had to wait till the 1920s- I remember the 40th anniversary, when some of the (usually dark green) buses (*) were painted white and gold- which soon looked a mess in the general atmosphere of filth that surrounded the city back then.
The gasworks was just off Regent Road, about half way along, and indeed by the old (Manchester, Bolton and Bury) canal, which however was closed and disused when McColl wrote his song. Trains setting the night on fire would have been travelling on Stephenson's Liverpool and Manchester line, or the lines out towards Bolton or Walkden.
As for axes tempered in the fire, I remember my father singing taht verse from Dirty Old Town in the early 60s (I would have been 9 to 11) while heat- treating an axe blade he'd found buried in the garden, by heating it red hot in the open coal fire, then quenching it in a galvanised bucket of water, filling the living room with sharp- smelling steam. Mam was out.
(*) Mostly Daimler CVG6 for afficionados