Luke:
Marvellous fodder for a project!

If it were mine, I'd barrel it up in the larger of the .461 Gibbs cartridges, impossibly long barrel, with sights and stock in the proper pattern.

Bramble might share this view too, judging from his previous post.

Read Seyfried's articles in the DGJ on hunting buffalo with this rifle/cartridge combination, and his Chobe Chicken-Hunt in Blackpowder Hunting magazine.

Chamber it in .340 Weatherby and we'll never speak to you again!

Seriously though, the list of common Gibbs Farquharson chamberings can be found in Wally's book, as previously indicated. Just choose your favourite within the constraints of the action size. I too am envious!