This whole area has been obliterated from its heyday as the centre of the Gun Quarter, mainly due to the building of the ring road/A38 during the '60s.
The first photo below is taken from Whittall Street, looking down towards the A38 and just behind, Vesey and Loveday Streets. Somewhere just beyond the large (green/white/silver) clad building on the left would have been the location of W W Greener's Prize Gun Works. On the right hand side where the multi-storey car park is located would have been the square with St Mary's Church.
This second image shows the corner of St Marys Row with Whittall Street
The image below shows a section of what is believed to be the original St Mary's churchyard railings.For some reason they have stayed put whilst all around has been destroyed! (Photo kindly supplied by Alan David). To locate them, they are roughly behind and to the left of the blue car in the picture above.
This contrasts well with a Phylliss Nicklin image showing St Mary's Row during 1963 with the whole run of railings intact.