If it is an original Farq., keep it original.
I notice you say Gibbs type - post pics and you will quickly find out exactly what it is from other NE members. You will see a lot of guns, such as the 1897 Westley Richards,called a Farquharson, but they are not.

A little pitting is a little problem. Non original barrel (especially in a very rare gun) is a big problem. Whatever you do, keep the original barrel.