As you are defining the difference in heat treated vs other...does the year or plant matter? I have read the article on bluing and looked into parkerizing. I read from natural "shiny" to dark gray.I would like to restore these pieces once and would like to do it right.
I used electrolysis to clean the parts. The spindles are a bright silver/gray. The tie rods, idler arm are dull gray with some dark shadows. That is straight out of the electric bath.
Since the parts were produced by a ton of different suppliers (depending on part) if you look across all the years there can be some variation but I would report that there is more commonality between the type of part and the original finish than difference. Some of the results may be due to the make up of the metal and its reaction to the batch while the variation can be a result of how fresh, old or burnt the bath oil is.
Some parts can take on a outer coating (for lack of a better term like spindles which are normally very dark in finish if you look past the 65-66 period while no change in surface is seen on steering components such as center link or tie rod ends. I believe that few if any are looking for an exact look (due to the number of variations) but instead a range - much like on other finishes such as sealers, sound deadeners, paint ....... I explain it as if a number of the experienced members here saw the finish and took notice that it "caught their eye" or stood out then its likely outside of the range your looking for
Most restorers have their own method on how to get - some can get pretty creative. As for your description of your spindles - other than the machined surfaces I would not think of them as bright silver unless its those surfaces that you are describing
Thanks for bringing my attention back to this thread - I need to follow up. Going to be a busy month but will book mark it with one other I need to get back to