Ok, lots going on here. First, it doesn’t sound like “bluing” was ever involved here. That’s a pretty specific process that only has 5 or 6 ways to do it and all of 'em are pretty specific. From your description, this sounds like blackening with motor oil- a process really similar to one that we in blacksmithing do all the time (we usually use linseed oil, but it’s pretty flexible).
On moving an oven close to the doors for a “quench” outside- prolly not gonna work because one oven is crazy huge and the other’s controller was having surgery last I saw it (on Saturday). They both run on 3-phase power and if that’s available near the loading dock, I don’t know about it (but I’m not saying it isn’t).
The good news is that it probably isn’t necessary. To get a good black, the metal really doesn’t need to be that hot, and you don’t need to quench all at once. It’s doable wit a torch and you can build it up in layers, sand/polish, all kinds of stuff until it looks like you want- and like I say, I think linseed oil is gonna do you much better than old motor oil.
I’m teaching induction forge tomorrow night if you want to chat about it. The class is at 7, I’ll be at the space a little before and for a while after.