For a single gauge, the Mopar SRT-10 A-pillar is a good choice.  Available
from Geno's Garage (http://www.genosgarage.com), it will replace the stock
A-pillar trim with one that has a molded-in gauge holder (this is used from
the factory on SRT-10 Rams to hold an oil temp. gauge).  It retains your
grab handle, so there's no downside to using it.

To match your truck's gauges, either a DiPricol (although some, myself
included, don't like the big white center cap) or an ISSPRO EV-series are
the closest match to the factory gauges.  I personally run an Autometer
Phantom, but that's because I went with a full compliment of Autometer
gauges.

As for mounting the thermocouple, you want it in the exhaust manifold, where
it will do the most good.  Drill/tap a hole right above the turbo mounting
flange, in the rear-most of the two passages.  This will measure the EGT's
from the rear cylinders, which run a little hotter than the rest.  Start
with a cooled-off engine, and duct-tape off the exhaust tip, then poke a
small hole through the duct tape.  You want to create some backpressure.
Next, start the engine, and while wearing gloves and goggles (or a
faceshield), drill a 21/64" (or 11/32", or even 5/16" will work - but 21/64"
is the closest to the 'correct' size) into the manifold.  All the chips will
be blown back out at you, so watch yourself (but better at you than into
your turbo).  Now you can shut the truck off, remove the duct tape, and let
it cool a bit.

Get a 1/8"-27 NPT pipe tap, and load up the flutes with grease.  Now
carefully tap the hole you drilled.  You'll probably want to go 5-6 full
turns on the tap to get the thread depth correct.  Turn the tap until it
gets a bite of the metal, and you feel good resistance to turning it.  Then
back it off 1/4-turn, and go forward again.  That will break the chip off,
and embed it in the grease.  You want to tap deep enough so that the probe
threads in 3 full turns.

Once that's done, just put the probe in, and hook up it's wiring to the
gauge.  Do NOT cut the probe wires to length - coil up the excess underneath
the dash.

For lighting, you can tap the larger-of-the-two orange/black wires from the
headlamp switch (this is the dimmer circuit).  For a switched +12V, you can
tap the red wire from the cigarette lighter.  For ground, you can use the
grounding screw on the lower dash frame, behind the knee blocker panel.