re:  what is the difference between the H3's and the H4s?

Well, in the context of the grilles, the H3s are the inner lights and
the H4s are the outer lights and you need two of each.  Actually, if
you already have round headlights you don't need to convert to H4
versions of the outers, but they are really better and worth it.  The
outer lights are 7-in diameter and the inners are around 5-1/2-in
diameter.

H3 and H4 actually refer to the removable bulbs that fit into these
light units (lens + reflector) and differ in that the H3 is a
single-filament bulb and the H4 is dual filament bulb most often only
used for headlights where hi and lo beam are required.  H3 bulbs are
used in both fog and driving lights--the design of the lens and
internal shielding around the bulb rather than the bulb itself
determine the type of light.  (The inner lights on the SA grille are
meant to be driving, i.e. high beam, and not fog lights)  "H" means
halogen, and non-halogen bulbs are often referred to as "tungsten" but
that is really incorrect as both types have tungsten filaments, the
difference actually being the gas in the bulb of the "H" bulbs is of
the halogen family.