Since I felt a little better today I went out and took a few photos to document this project start. The problem is the huge restriction for air flow from the grille to the engine compartment. This is also assuming that the engine compartment is totally sealed and all the air has to come thru the decklid grille like originally designed for an engine up to 90 hp or so.
I collected some of my junk decklids, cleaned the dust off, took some photos and measurements. You can already see what the problem is and how big (small?) the restriction is. No wonder my manometer gives me a vacuum reading in the engine compartment. You should notice that the lip that the grille attaches to also adds to this restriction. Please read the photo titles so you know what your looking at too.
I think I will conclude here feeling safe to say that the problem has been identified. Part 2 will be the process in measuring how much clearance I have to play with between the decklid rain guard and the engine components using the Bio Foam............Bruce