Here's the info you need about the upside down spring trick:
http://forums.stangnet.com/showthread.php?t=544275

"Latamud's" specification of a 60" link of all-thread must be a typo.
You need a piece just long enough to bridge the gap between your
existing spring pack and your auxiliary spring. 24" is more than
enough.  I have not read Latamud's how-to post in a while, but he uses
alot of words to describe a fairly simple operation.  You take the
smallest leaf from a donor spring pack.  You remove the center
through-bolt from your existing spring pack.  You place the donor leaf
upside down on top of the main leaf of your existing spring pack. You
use the all-thread to draw the two together, until they're close enough
to fit in a vise, then you use the vise the rest of the way and to hold
the springs together while you put in a new through-bolt.  I use a
longer than necessary through-bolt and add a spacer or built up washers
to the head end to make a registration stud for the axle bracket.  The
all-thread, I lock two nuts together at one end, put on a fender
washer, insert it through the spring pack and the donor spring, put on
two fender washers with motor oil between them, then another nut.  This
top nut is what you use for the tightening process.

It's really easy as pie.

You also need a clamp, for one end of the new spring pack only.  You
can make your own -- see the pic I added to the linked thread showing
how I made mine -- or you can go to a spring shop and have them bend
the square U-bolts like you can see on "Opentracker's" car in the
linked thread.

You may also need some new axle tube U-bolts, but only if your present
U-bolts have less than 1/2" of thread showing past the nuts.

The fender rolling, cut some slits every few inches on the fender lip.
Then use a baseball bat or a piece of pipe between the lip and the tire
to flatten the lip.

The 1" spring isolators will give you back more than 1" of ride height.
They don't cost much.  I would try this first, before rolling the
fenders.  OTPH, you should never have any tire to fender interference,
even at full compression.

Also, I assume  from now on you will be a vocal dispenser of words of
caution to those who cut coil springs.  I would never cut a half coil
at once, much less 1.5 coils.  I have usually seen a 1/4" drop for each
2" of spring removed.  And I drive the car around  for awhile to let it
settle before I remove any more.

Anyway, I'm glad to see you going lower. Unless you're scraping at
least once in a while, your Mustang is sitting too tall!

180 Out

Actually he increased the spring rate, ie made the spring stiffer by
reducing the number of active coils:

Spring Rate = F/S = Gd4/8ND3 where:
F = spring force.
S = spring deflection.
G = torsional modulus of the material.
d = wire diameter.
N = number of active coils.
D = mean (average) coil diameter.