The cold press illo board and the fact its unsigned (Joe signed pretty well everything as I recall!) mean I wouldn't touch it, personally.
I'd guess its some sort of student work from someone that attended the Kubert school, perhaps? It looks like it has age so I don't think its something done yesterday as a fake but rather someone practicing their own art by looking at Joe's.
A cursory Google search indicates Flaxon illustration board may not be readily available unless it's new old stock.
Even if you can't lightbox an image onto illustration board, you could always use a projector.
The blacks look very flat. Also, lines and figures on the left/right borders appear to be cropped way too evenly. Also, the bottom edge seems to folded over just a little bit. This may be a print that's mounted to the board.
Just speculation.
Love it. Thanks you guys! I also discovered that Al Dellinges use to do Kubert recreations. Interesting. Who knows?
Wow. Just noticed that it sold for over $1200.