Surviving baptism for children of John and Agnes all baptised in New Monkland
If John McEwan was 42 in 1871, that implies that he was born in 1828/1829.
John McEwan, son of John McEwan and Agnes Buchanan, was baptised in 1810, so he would have been at most only 18 or 19 when Jane Blackwood's husband was born.
I think the jury must still be out.
Have you found anything on John McEwan and Janet Irvine? Census? Death certificates?
