I wouldn't count on it.
The 3.0 and 3.8 don't use the same manifold gaskets, so the ports are either different sizes, or spaced different, or both.
Even if they were the same spacing and size, a set of Mustang headers is not likely to fit well in a Ranger.
If you do it yourself, I don't know what the cost would be. I can't even guess because I don't know what hard parts you will find worn or damaged when you get inside.
I just priced Ford reman for my own Explorer, and my price was just under $2700, and that's with me installing it.
It was a Euro thing. Apparently, from what I have been told, that was how it was done in Europe at the time, and Ford thought it was going to catch on here, so they tried to do it, and being Americans, we hated it.
I agree, as a flip it isn't worth it and will be hard to break even.
As a tractor to have and use, if I had enough land to need something that size I'd hop on a running 8N for $1000 all day long. As it is my 855 is plenty for my lot.