My GGGG grandfather, Dr. John H. Bush ( ca 1770-ca1832) was married to Mary Rowland, the granddaughter of John Blalock (died 1791 Newberry Co., SC). He was from the same Blalock family as your side of the Blalocks.
A George Bush was a brother in law or very close friend and neighbor to Peter Cash in Stafford Co., VA ca 1738. This is the same Cash family that later married with the Blalocks.
And finally (?) The descendant of Abraham Bush (d. ca 1690) Lancaster Co., VA, John Bush had descendants that married your Bruce family.
You should have come across the Bush/Bruce story when doing your Bruce/Carroll digging!