50x66 Foamcore

Acrylic products are available in 60 and 72 inch widths. I have never heard of 60 inch foam boards. You might have to re-evaluate your substrate material. I hope someone else has an answer other than mine.
No answers here, just more questions.

I am interested in your two choices: acid-free fome-core or Gatorboard. My understanding is that Gatorboard is not an archival material by any stretch of the imagination.

In other words, if Gatorboard would be acceptable, why not consider regular fomeboard (which, as far as I know, isn't available bigger than 48x96?) :(
If there is no need for archival substrate I would check with some of your local suppliers of paper goods to the printing industry. There was a product that I got locally from Mac Papers called Kappaplast that was similar to Gator Foam and if my memory serves me right was available in 60x120.

Edit: I just went on Mac Papers web site and found 3 products by Gatorfoam that would be big enough; all the same size and 3 different finishes (white, black and natural).
I just need a smooth porous surface material. AFFC and some Gator boards have a porous surfaces.

Thanks everyone.