Hi Corby,
these I think are the facts I can offer you.
The picture appears in SAE paper no 670065 February 1967.
entitled;
The Ford GT Sports Car
by R.C.Lunn
of Ford Motor Company.
It is a full page picture on Page 20 as Figure 33 captioned; 'Final Layout of Components for the MkII.'
the preceding paragraph is;
'All of these changes were incorporated in the vehicles that made their first appearance at the Daytona 24-Hour Race on February 5-6, 1966 (Figure 33).'
As to what your picture is worth, well, if it is an original pencil sketch, and if there was some identification on it, then it would be worth a lot, but if it is just a copy, you could get one from the SAE paper, now $15 from SAE. I myself have an A4 laminated copy I prepared for my wall from the SAE pdf, because I liked it. The picture in the SAE paper is full page, so quite acceptable quality for copying.
So is it an actual sketch?, or if a copy what kind of print and paper?
regards
Dave