Hiya,
Unfortunately there isn’t a connection.
John Neilson didn’t have a middle name. I've got his original birth/marriage/death certs, as well as all the original insurance policy documents he had over the years, and none give a middle name.
They lived all their married life in Port Glasgow. Margaret Spence died in 1946, and her husband, John Neilson died in 1957, so its not possible that this couple would have been your grandparents, as you mention your grandfather died in 1972.
Gillian