What if I already own an intercooler from a '87 or '88 thunderbird turbocoupe?  Can I get some kind of discount?

I have always planned of offering a kind of core charge credit for anyone
who has already obtained a Turbocoupe intercooler.  I am planning on
offering a credit of $100.  This is a difficult figure to come up with since
I bought one from a junkyard for $40 (since the guy thought that it was a
heater core and I could explain to him what an intercooler is,) but I have
also paid as much as $125 for one. It doesn't seem too tough to get one for
about $100, so this is the price that I arrived at. 
 

Do you have any figures for the horsepower gains or inlet/outlet temps?

No, I have been unable to get any hard numbers yet.  There are a couple of reasons for this.  I used to have an intercooler temperature in and out gauge fitted long ago, but I have lost one of the thermisters and cannot find a
replacement for it.  (Actually almost nobody knows what a thermister is, but
it is some kind of fast responding thermocouple, the company that made the guage is no longer in business.  It was called Auto Avionics)  I had a great chance at offering my kit to be dynotested on a mustang SVO that Jim Whelan with Motion Dynamics was going to be testing.  After coordinating with him for more than two months, I ended up going up to Ft. Worth Texas to buy a Merkur a couple of weeks ago.  This turned out to be the weekend that he finally did his dyno test and I missed his call. I plan on doing this test the next chance that I get, and I will publish any numbers, good or bad.

IS the kit complete?  What about written instructions? 

This kit is complete.  It has more than 35 pieces and includes the bolts, gaskets, hose clamps, adapters, etc... everything.  The instructions are quite detailed with some photos showing the installation of the more complicated portions of the system.

How long will it take to install?

For someone who is familiar with hand tools, this installation  will probably be one of the easiest bolt on modifications that you will do.  The toughest part will be rotating the turbocharger housing to
fit the intercooler. This is actually very easy.  You will loosen the
six bolts on the compressor (cold) side of your turbo.  Then the turbo
will rotate about 60 degrees.  You will just rotate it till the intercooler fits perfectly.  Then tighten them up.  All of the rest is no tougher than hose clamps and screws.  I will time it when I install mine, but I am betting 4 hours if you go very very slowly and carefully.