Er ... they could hardly get married by 1872 if they were born in 1883/1885

I see from the 1881 census that they were aged 47 and 48, so (if that is accurate) born 1833/4 and 1832/3 respectively.
They had daughters Mary, 26 and Helen, 21, both born in Scotland. In 1871 their ages were given as 15 and 10, so they were born about 1854/6 and 1859/61.
You are in luck because Mary was born in Glasgow on 17 September 1855. 1855 certificates contain lots of information that was not recorded in any other year, so go to
www.scotlandspeople.gov.uk SP, buy some credits and use some to view that birth certificate.
In 1861 there's a family in Glasgow consisting of William L, 28, rope maker; Helen, 29; Mary, 4; Agnes, 6; and Helen, under 1 year. Helen senior was born in Stirling and the rest in Glasgow.
In the church records at
www.scotlandspeople.gov.uk there is a record of their marriage in Glasgow on 17 November 1854.
In 1851, in Glasgow, is a family consisting of William L, 46, quay labourer, born Stirling; Agnes, wife, 55; William, son, 16, jr ropemaker, born Glasgow; and two servants. So it looks as if this could be your William. I have yet to find them in 1841, though if Agnes was his stepmother rather than his mother there is a possible family with mother named Elizabeth. There is a baptism of William, son of William Livingston and Agnes née Livingston in Glasgow on 23 October 1834.
In 1851 there's a Hellen Wilson, 19, born Stirling, servant to John Geddes in Glasgow. She could be the daughter of William Wilson, 40, and Isabella Wilson, 40, in the 1841 census aged 9. Like her sisters Isabella,7 and Margaret, 5, this Helen W was born outside Lanarkshire.