Might be a good idea to include in the first post if it was a PS or non- PS box so that others will not have to look up the codes to see if these apply to their application
Since it's dated Sept 68 I'm guessing you have a fairly early car
what finish should the small lock nut be on the sector shaft adjusting screw be ?
Adjustment shaft in #1 would have been IMHO dark heat treated bare steel like the cover bolts. The nut could have always looked to be fresh bare steel -
Vent is bare steel I believe
The cast center in #2 is just that cast iron while the steering shaft would again be dark heat treated. Believe the large ring/nut was just bare steel though I've never had it tested
would it be correct that the rest of the box is all natural ?
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The case would have been a combination of natural cast and shinny machined surfaces (mounting pads, cover mating surface, area under and around the large ring/nut at the shaft). Then you look at the other pieces such as the cover (bare bar steel) end cap (zinc and so on)
Paint marks appear to match others of about the same time period. Would have been marked at the supplier not the assembly plant.