Really not that easy to setup a material, like pewter... I want to do a pewter material for unity/alloy shader.
In SD, there is the node for setting a custom IOR value.
The right value can be obtained from the list, you linked.
I supect the output value (a RGB color) of this node to be plugged into the "specularity" channel of alloy shader.
But the thing is, alloy only takes that speculartiy into account (use it) for non-metals.
Like when alloy shader registers a metallic input (white) in the other packed channel, specularity value is ignored for
that areas.
In case of a nearly full metal material, setting a specularity/IOR value would make no sense at all, because it will
be ignored...
So I am at the same point, as I started on how to create a pewter material - maybe I just should not care about what is "correct"
and just take some aluminum material and tint it a bit and so on...
edit: I´ve found, that Titanium is close to Lead, regarding IOR