Alot of (black)smiths took work on the railroads..
Molly is hard as I doubt Molly was a real name.
QLD BDM and NSW BDM are both online (for those years)
YOu could search for any marriages/deaths for her to SPENCE or as a SPENCE.
I tried checking 1930 NSW Electoral Rolls but without a 'real' first name there are just too many to go through all of them,,,,THAT is even if she was still a SPENCE or at the same address in 1930.