Still looking...so far I found two options that I believe it could be;

John born 1760 in Westbury to Samuel & Mary
John born 1762 in Westbury to John & Mary

I found a couple of Family Trees on Ancestry which mostly has John's parents as being:

Samuel Hayward 1721-1797 married to Mary Parry born 1734

Though, not much documentation to verify.

Hoping it's Samuel and Mary parry as their tree goes back another two generations!