Amarillo,
I don't have a bore gauge, but ID leg calipers that can reach in 3 1/2" in a 12 to get diameter. It's within + or - 1. When I drag the calipers out slow I start to get a drag at about 2" so that must be where the chokes begin on my 1903 1900 damascus that has .730 bores. What are the bore measurements on your 1889?
The rib on my 30" 1900 looks like stallone's 1889.
I have six Elsies from 1892 to 1942 and all the bores are from .729 to .731.
I don't know what is meant by keels unless it is a triangular piece of metal between the barrels and rib rather than all filler. To me it's just a filler. There is no 'keel' on Hallowel's definition page. Maybe the gun in question does have .710 bores; who knows.
The only Fox 12 I owned was a 1929 Sterly with .725 bores.
Dave Katt; I think you are confusing muzzle measurement rather than bore. My Baker Batavia Damascus has .727 bore.