I like what you've done, especially with the random spare parts!
I think you'll need larger pieces to make the belly pan worthwhile (though it's a good start) and the grille block probably isn't doing much of anything.
When the air hits your inset grille block it will want to go sideways, right into the side intakes. What I recommend is taking that off and mounting a new, two-part piece flush to the rest of the bumper (Cut it a little larger than the opening and it will easily lay flush) and on each side. That way, air entering at the centerline will still go into the grille, but air coming at the car from a foot or two over will hit an uninterrupted smooth surface all the way to the wheel well.
Visual.
Edit: oops. Didn't see it's a '95. If you don't use the fogs just block over them too. If you do use them block them with clear plastic. I've found clear plastic basement window covers work well for this and are half the price of acrylic.
Also, aero wheel covers and rear wheel skirts will help you. Do the grille block and belly pan first though.