The issue is that while Amos is a tail-ender, we've no way of picking out which Smith-Smith births prior to (the early 1930's) have a father called Natty/ Nathaniel.
Add to that the parents of the 1908-born Nathaniel appear to be living as Johns in the 1939 (see reply #8) it's far from straightforward.
The best candidate for Amos Smith's birth is 1934 Wolverhampton. You could try buying that one if the father is named as Natty . We can rule out 1932 MMN Finch as the cert is published online.
Go back to Nathaniel's 1991 death and see if there was a notice/report in the local newspaper, or find out where he is buried and go look at the headstone/find out who else he's buried with.
In the meantime, get that order in on your Maternal grandfather and grandmother.
Pauline