I'd imagine that at the least, the bolt face would have to be modified to accept the larger rim on the 44-40. COL is the same at 1.59 for both cartridges so that won't be an issue. If your B92 is like my Navy Arms 1892, a 44-40 round won't fit in the smaller 357 magazine tube even if you could get it through the loading gate which appears to be a very tight fit at best. I'm not sure, but wouldn't be surprised if the carriers are different between the 357 and 44-40.
Not saying it can't be done, but I'd think you'd be better off trying to convert a 44 Mag or 45 Colt or just buying a 44-40 to begin with.
Regardless, I'd still get the B92 as a 357 lever gun is one of the handiest rifles to have around.
BTW, how is the Vaquero 44-40? I've got a 7 1/2" one and I'm not very enthused with it.