???? - Not sure what you are saying; any of the .450BPE work just fine with a "standard" .458" groove barrel and the straight case .450 are certainly less costly to obtain reloading components.
The "reason de etre" for the necked Westly-Richards Express cartridges was so that an express load cartridge could make it around the corner and chamber in a Martini type action, the various long straight Express rounds could not do this.
Normal dropping/falling block or break open actions of course did not have this limitation

To be sure, the .450's in the 1800's were all over the map as to bore/groove size but the (mostly) paper patch bullets would bump to whatever bore size upon firing.
The easiest and still "period correct" .450 Express would be the plain old .450 3 1/4" BPE, and you would not have to greatly alter the extractor.

BTW: My Cogswell & Harrison (Martini type action) .500/.450 No.1 of approximately 1873-75 vintage has a chamber neck diameter of .498" which was needed to accomodate the early rolled brass cases. Bullets would still have been anywhere from .450" to .458" diameter depending upon patched or greased and my barrel groove is .459". Shoots exceptionally well using the RCBS 300 grain .458 gas check cast 1-20.
I only neck size about 3/8" of the neck to hold the bullet and anneal every 3rd firing. Brass still doesnt last very long before neck splits.
- Mike