Hi,
I don't know if this will narrow down the choice of William Gurnhill's but there is a burial of a William Gurnhill at Glentworth in 1879 aged 79 (i.e. born c1803).
On the 1871 Census there is a William Gurnhill, born Blyton, at Glentworth with a wife called Susan.
Possibly this is the William Gurnill baptised 11 Sep 1803 s/o Robert & Ann Blyton that Beady found so you could maybe eliminate him.
Gill