Hi there,
I can't find a marriage for the two, but from a few of William Munn and Mary Dykes' children's birth/christening records, their full names are given as William Lang Munn and Mary Auchincloss Dykes.
There is a 17th May 1804 christening in Paisley for William Lang Munn to parents James Munn and Janet Sclater. There is also a marriage for the 2nd June 1787 in Paisley for this couple.
For Mary, there is two possible births/christenings; one in 1804 and the other in 1809, both to parents James Dykes and Agnes Leyel (or Lyle). Again, there is a marriage for this couple (Agnes is listed as Leyle this time) for the 28th June 1800 in Paisley.
Hope this helps you get back another generation!

hume24
Interesting thread, detailing this family:
here