.461 Gibbs would only be a problem as to the logistics - finding a reamer, purchasing the - expensive - brass, new barrel fitted and contoured. Loading and shooting it would be the easier part.
If MBL, it should have a straight buttstock, no pistol grip. If it has a safety, you could probably also make a nice back-position creedmore-style target rifle out of it (keeps one from blowing some toes off...)
Whatever you do, I would opt for a Brit cartridge - such an action deserves to be shot with a brit cartridge, and not something like a 45-70!