Hiya Dave
I've found a William & Margaret Clark both aged 44 both born Glasgow in 1871.
Wm is a porter at post office, no family listed.
131 Canning St Bridgeton, Glasgow Calton.
Same couple, he's a bagman at the G.P.O are 54 in 1881
168 Gallowgate, Glasgow Blackfriars.
ozn