re:  What I need is the "combo" 5 1/4" + 7" bucket that is ONLY
available from South Africa

On my Joel Cohen setup, the "bucket" is NOT a combo.  I believe this
is the SA setup and it uses the original outer 7-in bucket as came
stock on early Vanagons everywhere.  There are separate galvanized
sheet metal brackets for mounting the inner lights.  The lights
themselves have three mounting tabs welded to the reflector and the
lights are mounted to the bracket with a system that permits some beam
adjustment.  The brackets are essentially rectangular with just a
round hole in them to clear the back of the light.  Not something to
normally call a bucket.  The brackets will pop-rivet to the body
work.  Since the grille opening is not straight-across, there are left
and right brackets.  The brackets should be worth around $25 each (a
SWAG).  I'd look really closely at a first generation Golf (Rabbit)
convertible with the 4-headlight system because I think the inner
lights are much like those and wouldn't be surprised if the mounting
system is similar.  I haven't done this, so another SWAG.  The
diameter of the light units is indeed 5-1/4 in, which is not the same
as the universal four headlight system now hardly ever used--those
units are 5-3/4 in.