Saying someone was born "abt" a year, rings alarm bells as that is usually how submitted records on the IGI are written.
These are often just guesses sometimes calculated from year of marriage or births of children for example. Even worse, some appear to be simply invented. These unproven guesses are then added to people's trees and taken as gospel by anyone tracing this line.
I don't know how to suggest that you check these as I've never traced back that far myself.

I've had a quick look and can't see anything that mentions how early the PR's for the area begin.
I don't think there is anything here:
http://www.kilsyth.org.uk/history.html but there may be someone you can contact who can point you in the right direction.
As well as just looking for the marriage, my suggestion of looking for the children's baptisms, and maybe Jon's death may lead somewhere?

But, frustratingly, there may be nothing there to be found ....