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I'm no heat treating guru, but looking at the one picture I'd say there already pretty much annealed. But I know how you meant it Magicniner.
If the parts were made from common off the shelf mild steel then it's highly doubtful any form of heat treat was ever performed since as others have mentioned the carbon content is already too low to do so unless something like pack case hardening was done. Logically that being done since it's usually for wear resistance doesn't make much sense. About all I can see is the originals can be used as patterns for all new parts being fabricated, machined, welded as the first were made. Again I could be wrong, but I know of no way to return fire altered mild steel to it's original condition in a viable time and expense method over just remaking all new parts. Yes I get that keeping it as original as possible is desirable, but very little of it is ever going to be again.
Magicniner wrote: ↑Sat Aug 31, 2019 11:00 am
Mild Steel does not have the Carbon content to allow heat treatment other than annealing when it is work hardened.
And yet;
The previous owner of my place was a farmer / bricklayer. He left some old tools behind, including some spikes made from re-rod.
The pointy ends have been hardened; I can't say how hard they are, but a lot harder than mild steel re-rod.
Only the end few inches; the rest is good old soft mild steel.
Magicniner wrote: ↑Sat Aug 31, 2019 11:00 am
Mild Steel does not have the Carbon content to allow heat treatment other than annealing when it is work hardened.
And yet;
The previous owner of my place was a farmer / bricklayer. He left some old tools behind, including some spikes made from re-rod.
The pointy ends have been hardened; I can't say how hard they are, but a lot harder than mild steel re-rod.
Only the end few inches; the rest is good old soft mild steel.
Rebar is often Mystery Metal, so if it's hardened, and that's not due to localised absorption of carbon from a forge or fire, then it is by definition not mild steel, whatever you choose to call it.
Mild steel doesn't mean it's soft, it means it's carbon content is not in the range which will allow hardening through heat treatment
I would be pretty surprised if any of the chassis or brackets were hardened. 4130 didn't really start to show up in racing until about that timeframe - mid 1950's from what I've read. What is it that makes you think that brackets were heat treated then?
Stamped and formed brackets and panels in Mild Steel exhibit Work Hardening, not Heat Treatment, but annealing them returns them to the soft state losing any additional hardness and rigidity afforded by the Work Hardening.
But I know how you meant it Magicniner. 