The Ford Barn - Header cover panel and windshield opening

I'm not certain that photos show what I need to depict, so here are actual dimensions. Sorry, but I can't rotate the header panel sketch 90*. As you look at the drawings note that my scale is 1" = 1/2", ie double size--easier to see the whole picture. If you print the pages they align perfectly if you match E on the header panel with e on the pillar sketch. My questions are these: One, is section A of the header panel supposed to be flush with a, the face of the A pillar ? I think so, but I need corroboration. Two, when in place does the U channel (CD on the header sketch) lay behind point c on the pillar sketch? If so, the 5 holes on my new header align with the back edge of the angle iron shelf, and I know that is not correct. In summary, the front to back depth of the A pillar (a to e) is 1 1/2" and the depth of the new panel (A to E) is 1 7/8". If, in fact, A is supposed to correspond with a, and E is supposed to correspond with e, then my new panel is 3/8" too big. The next question --is the extra 3/8" in one location, or is it an accumulation of excesses in several places? Assuming that there is more than one manufacturer of this repo part, is there one out there that is truly correct? I don't wish to bad-mouth my source, but I haven't been in this hobby long enough to have purchased from many different vendors. If there is not a 'more correct' part, I can modify the one I have if someone can tell me where to start cutting. Thanks in advance for guidance.