I don't know much about S&W's chambered in 455, but I suspect he's got a S&W mkII, so that would mean it's chambered for 455 webley, unless there's something I'm missing.
Basicaly 455 colt and 455 webley brass are almost the same - colt brass is just a little longer. In reloaded cartridges the colt might be longer as well, but I've never seen it.
455 webley was for quite a long time loaded as a very deep hollow based bullet to allow for even expansion. If it's being reloaded it's worth looking for, but you can get away with a mildly inaccurate soft cast flat base 45 cal bullet if you're really stuck. For components - mystic precision and henry nierychlo (spelling?) are both board members and very helpful and knowledgeable.
Fiocchi also still makes 455 webley ammo that's relatively rare and higher pressure, but should be fine in your friend's gun (it's a bit much for antiques sometimes, but still not bad... just not a light load).