Chrome is best thought of as a clear coat for Nickel. It adds a blue tint making the nickel brighter and it seals the Nickel against tarnish.
This following is not a hard fast rulle, but a generalization.
Typically on the A for 30-31 the inside stuff was nickel and the outside was chromed.
For 28-29 they used nickel on the outside parts.
It needs to be understood about Nickel plating. Generally speaking there are 3 types of nickel. There was the early plating that pre-dates the 1930's and then a second commonly used Nickel. Both went on dull and needed to be buffed out. This is seen on the back side of bumpers and cabriolet landau irons where you get the grey color.
Much later then the 1930's they added oxidizing chemicals (per one plater I talked to) that gave a bright nickel plate that does not need to be polished. This is what most shops use today as it is less labor intensive. Bright nickel plate was not an option during the A production period.
I would venture a guess Ford might not have gone to stainless if you had bright nickel. While the stainless was a more expensive material it was much less labor intensive (read much less $$$ and less workers).
