Obviously, there are many more than two Gibbs Farquharsons with Selous plates so the consignor is in error on that point.
The rifle must have been chambered in 461 No.2 originally as that rear sight with the black powder charges and bullet weights conforms with the No.2 loadings. The gun looks to have been rebarreled while utilizing the original rear sight and as stated the forend is an obvious replacement.
I would like to get this rifle and put it back to its original configuration. That would be the only just treatment for such a rifle IMO.