The 450 Marlin now there is an Alaskan Bear rifle, if there ever was one. So many ideas come to mind with a left handed BAR.
In addition to the already mentioned 450 Marlin, 358 Win, 350 Rem. Mag.,; there are several others that come to mind: the 35 Whelen, the 338-06, the 416 Taylor. If you really want to wild as in wildcat you could use the 325 WSM case as a necked up to 338, 358, 375, and 416. I'm especially fond of the WSM case necked up to ta 416. With this much powder capacity it should e capable of pushing a 400 grain bullet to just over the magic 2,400 fps that made the 416 Rigby famous.