Paul
There are (were) several different versions of the MK I, including
two different nostrils and three different rear ends.
Best bet is to get a hold of a couple GT40 books.
For huge/detailed pictures, you can't beat " The Ford that Beat Ferrari",
which was just re-issed. It's not cheap at $ 80...but it's worth it.
I also like John Allen's GT40 books...which are filled with color shots
and very reasonably priced since they are soft cover.
The Shelby GT40 book is also good...but not as much detail.
Good luck.
MikeD