I'm almost certain that the nuts which hold the front manifold to the y-pipe are M10 x 1.5
Mine were rusted insanely as well. The stealership i went to couldn't find them on the computer. Went to a couple stores to try and find one....one guy referred to the nut as a "jam nut" apparently its kind of like a locking nut. My dad works for ford, luckily he was able to find me a replacement at one of the labs.
