28" barrels is what the book says that serial number should be wearing
as for the black what ever
the first thing I would try is a solvent and a frontier pad
http://www.exploreproducts.com/big45...un-cleaner.htm
they clean great but will not damage the blue or case colors (steel wool will) try to keep it off the wood - masking it might be a good idea
as is - looks like a nice shooter