One thing you would need to check, which would be easy for a gunsmith to fix, is the rim thickness of the 416 Rigby Vs the 460 Wby and also the extractor groove diameter.

I have a suspician that the Wby has a thicker case rim than the Rigby in which case the extractor would need to be thinned a little bit.

If the Wby extractor groove is deeper than the Rigby then you might need to get another extractor from say a 375 or 458 because if the Wby extractor groove is too deep then the cartridges will fall out if you pull the bolt back slowly.

There is one chap on AccurateReloading who posts as RIP and he has a CZ that was 375 H&H and has been rechambered to 378 Wby and as far as I am aware it is a fully fuctional rifle.

Another option that you might consider is 450 Rigby if you are only going to shoot reloads. The 450 Rigby is basically a 416 Rigby Improved necked up to 45. Brass and ammo for the 450 is bad news. To make them from 416 Rigby you only need to expand the 416 to 475 or 50 and then run them through a 450 Rigby die to give you a little shoulder and then off you go. There is a fellow on AR who posts as OldSarge and he has a 458 CZ (or BRNO) that has been rechambered to 450 Rigby and had quite a few things done to it and he wants to sell it.

Apart from the simple conversion there is one other reason to consider the 450 over the 460 Wby. The 460 has huge freebore, I mean huge freebore, the rifling starts about .8" from the case mouth. If the gunsmith has a reamer that is not full on specification then the freebore diameter might be cut too large in diameter and you will pull your hair out trying to make it shoot. If it is done right then 460s seem to be about the most accurate big bore of all.

One other disdvantage of the huge freebore and this applies even if it is done at the right dimensions. If you want to play around with a lot of reduced loads, especially loads that are under the 458, say loads that might equal top 45/70 loads, then the 460s big case capacity and huge free bore can and does cause hangfires and especially with lighter bullets.

Although in America you have a powder which I think is called something like Accurate Arms 5744??? which is a reduced load powder and is basically 4227 burn rate but is big and bulky and easy to ignite liike a shotgun powder. That might allow loads in a 460 with lighter bullets at top 45/70 loadings without hangfires.

The 416 Wby is different as it does not have the very long freebore of the 378 or 460.

Have fun.

Mike