Just checking, will a 416 Taylor reamer clean up a 30-338 chamber?.....obviously different bore.

Roger

Not unless you advance it a bit; the case body is the same. But actually the chamber body doesn't need to clean up unless you just want it to. So just get a throated/necker and use that.
I like to have a new chamber too, to make sure it is concentric. Don't know what the last guy did.
So, no.