This page features the building at 19 Salmon Street, starting (from the left) at the extension of Tarver Street, moving to the right and finishing with Plummer Street.
To help you focus on the small area, here are extracts from the 2 old photos on the previous page:
 

Here's a sequence of photographs taken in April 2003, by Geoff Birchall.
Looking along the side lane (extension of Tarver Street):

This section at the left end makes it appear to have been the main office.
Notice the clock above the doorway, and the bottom of a flagpole on the other facade.

The final 3 pictures were taken from the Plummer Street corner.
Notice the flagpole in the distance.

Many thanks to Geoff Birchall of EDS (working at GMH) for these pictures.
At the time (April 2003) he also referred to other car plants:
"... Holden's (at the other end of Salmon St - where I have worked for 27 years), and the old AMI plant where they used to build Triumphs, Vanguards etc. (My first cars were Triumph Mayflowers)."