Hi Mark
I appreciate this 'post' is by now very ancient but just in case you haven't found out what you requested I have added it below. Sadly the images of Cawston marriages do not begin until 1754 so I cannot help re Robert Nichols marriage to Sarah Porter, however, the marriage dated 1787 is viewable. The marriage between Robert Nichols and Mary Clarke took place at St. Agnes' Church on 18th July 1787 and was signed by the parties. It was witnessed by Thomas Clarke and Mary Saul. They too signed their hands.
Hope this is of help?
Meslc