Interesting find Melisandre but it contains a couple of glaring errors. The "St. John's Works" was in Queen Victoria Road, opposite the Rover factory and on the site later occupied by the GPO sorting office and drill hall.
The Dingley Bros Viaduct Works was at 74 Spon End, next door to the Black Horse Inn. Many people might remember it in later years as being the Victoria Wines off-licence.
The Viaduct Works (also known as "Ivy Cottage") is just visible on the extreme left of this picture, set back from the road: