Is there actually wood under the label of a Don Thomas Clasico Box?
Working on my second build. First build with a bolt on neck. When I drilled the holes in the box for the hanger bolts it sure looked like cardboard.
I don't know about that particular box, but I built one out of a CAO box and I think it was like a cardboard on the sides, not sure but it worked and is still playing. I'd just brace that side pretty good with some real wood. You would have to do that anyway.
Don't be instantly afraid of a pressed/cardboard top, I've made some that sounded very good.
It's not wood and will never be...but don't give up on a box (or it's sound) just because it's cardboard. You can always make a small sound hole bigger.....but you can't make a big one smaller...luck