Closest thing to a non Kenner proof card would be something like these Grant:
http://theswca.com/index.php?action=disp_item&item_id=73244
It's a Made in Spain sample card sent to Kenner for approval.
Mattias owned a Made in Mexico sample card too, similar deal.
And then there is this: http://theswca.com/images-packa/toptoys-presentation-board.html
I think copies have been made of this though and I was never really 100% sure about it but it is still on the Archive and it was discovered by someone with pretty good rep so likely legit.
Also, unless I am remembering wrong there might be some Meccano 2D pre production stuff, thinking it might be printing plates or something for the 12backs? Memory fuzzy on that one.