Ok here are some pics of the most current updates.
I installed the lower partial grill block. Will watch temperatures and make sure everything is good.
Open in center for partial flow:
Full under belly pan. I did notice longer coast times, and maintained speeds.
Next I constructed a rear diffuser out of coroplast. I mounted it tonight.
Also visible above is the belly pan which goes all the way back.
I averaged 52 MPG on the way to work today, without the diffuser or lower grill block.
Aside from the trunk lid extension, I think the mods are at their peak. Not much more I can do. Aside from rear wheel skirts, which I wont do; they will never look OEM.
-Alex