RE: 336 in other calibers
that gun is designed primarily to handle rimmed cartridges and also it's pressure limitation preclude the 50,000+ PSI cartridges as you mentioned.
Other levers are much stronger such as the Winchester 88, the savage 99 and the Browning BLR. The latter is the only one still being built which suggests that there's not a large market for those cartridges in a lever.