I have a High Wall Traditional Hunter that started life chambered in .50-90 and is now heavy barreled in .50-140 (3 1/4"). The action is strong enough to load to .500 NE levels, at which I believe the cartridge becomes the .510 Nitro Express of D'arcy Echols and Bob Schneidmiller fame.

However, if I wanted to shoot full power loads frequently, I think I would need to restock or do something about the crescent buttplate LOL.

The Ballard Rifle Company will build you a High Wall in any caliber up to the .600 NE, although I believe for that and the .577 NE they use a slightly larger/heavier receiver. You should be able to modify any modern Miroku high wall Winchester 1885 or Browning 78 action up to fifty caliber and barrel as you see fit.