Hi Nick, there are a number of Shapland Wills on the National Archive website which you can download free once you create an account. They pre-date the John you refer to but may help to untangle the earlier branches. They include the will of a Christopher from 1593, quite an unusual name which may indicate an earlier connection to the parish.
In regard to the marriage, the tiny neighbouring parish of Twitchen could have been another place for the marriage, but registers only start from 1700 (approx) I think. There are likely Bishops Transcripts from earlier which may be worth a look. Regards, Paul