I would wait for the Mantle experts to add their opinions to this thread. I don't get autographs validated, and I never buy pencil cuts, but if this one dropped in my lap and the experts said "good", I think I would send that first page to SGC. If they liked it, ask them to remove the cut and slab it. Maybe that's a bad idea, but that's my thinking.
I do have a bunch of 'sort of valuable' cuts at the moment, and I've wrestled with sending some of them to SGC. But that would make me a hypocrite
. Personally, I see no value in owning a cut that comes with a piece of paper authenticating it;however, a uniform-size slab would make it presentable.