Lionel #6530 "Prototype"

You truly have a unique piece. You may have discovered a previously unknown sample. 

Unlike a lot of "factory errors" or "prototypes" I see, this one reaks of the real deal! Excellent find!

Very cool

My guess is that it is a first stamping of the lettering.  3530 was out of production by the time the 6530 was being made. So Lionel must have had some 3530 shells around so the tested the heat stamp lettering process on a painted over shell. To me a prototype has decals or glued paper for review.  Nice piece, and odd because it is a 3530 shell stamped 6530. You see where Lionel used up old production items, like the 1955 version of the black and yellow painted Virginian Trainmaster, but that was not pre stamped. Early 1960's times were getting tough for Lionel so any penny they could save was an opportunity.

Just my opinion, great item and is a jewel to any collection!

Madison purchased a lot of stuff like retreads from Lionel, remade them, rebuilt them and then sold them. Making unique Lionel products,

I don't think it's a prototype, because the white lettering appears to be heat stamped. I do think you have an unusual piece that many collectors, myself included, would be happy to own.
Back in the crazy days, who knows what sort of money it would have fetched. Today, who knows!?!

Lionel did repaint shells and frames on occasion.
I doubt it was put together by Madison Hardware.

You mention - (Although Greenberg mentions something about a "prototype" in another volume which I don't currently own). 

Have green greenberg's volume 1 in it under 6530 at the end of description it mentions this

See also factory prototypes and errors in volume II,behind the scenes (second edition).

Perhaps someone here has that edition and could post what it says or maybe that edition could be found at one of the large bookstore where you could look it up .

Hope you find out what you have if you do please let us now.

Thanks

Here is a page scanned from Greenberg's book.