I did this in my Jeep XJ, and now I've doing it in my bus. I deleted the in-dash radio and replaced it with a Google Nexus tablet computer. This functions as a real-time engine monitor, as well as moving-map GPS navigation. I can also link this tablet to my iPhone for internet access, so I could theoretically surf the web... or watch movies, youtube vids or porn while driving down the road. Of course I never do this. Might get arrested, go blind...or worse.
For music I installed an amplifier, connected speakers, and connected a $30 USB-powered bluetooth adapter to the amp's input. This allows me to link up my phone and stream Pandora One ($5/mo, no commercials), play content stored on my phone...or link up the tablet and play content stored on that. I no longer have a radio or CD player...but I no longer have a need to carry CD's and there's nothing but stupid sh!t on the radio anymore.
I connected a bluetooth OBDII adapter to the port under the dash; it links to the tablet and allows use as a real-time engine monitor using Torque Pro (available at the Google app store for $5) Powerstroke diesels have a shitload of engine sensors and Torque Pro has a predefined set of PID's for Ford which will read them. You can add, delete, configure all kinds of different instruments all kinds of different ways. Graph trends, data log, add inputs...I've just scratched the surface with this app.
For navigation I use Backcountry Navigator (paid version), which allows map downloads at varying zoom levels for offline use (when you have no connection). To download I will pull up behind the house and pull wifi signal from the house router. All kinds of possibilities w/ this app; again I've just scratched the surface.
For city navigation I can link the tablet to my iphone and use Google Maps...or just use my iPhone itself.
Google Nexus 7 has a really good internal GPS antenna; much better than most tablets according to my research. The 2nd gen Nexus 7 can be had used on Ebay for damn cheap; I paid $60 for a used 32GB wifi model.
OBDII adapters have come WAY down in price; this one here is reputed to be good and is 9 bucks on Ebay. 9 bucks. Amazing.
For a mount I cut out a piece of plywood (4" x 7.5"), countersunk a couple 5/16 bolts, which go thru the plywood and thread into a piece of 2"x .250" aluminum stock that's about half an inch longer on each end. The longer ends grab the dash inside the hole and clamp the plywood firmly to it. Then some industrial strength velcro from Lowes. 3" x 4" works nice on both sides. In this pic I have yet to velcro the plywood. You can see it on the tablet laying face down below it.
Here it is on the dash:
Instruments I'm using:
Engine coolant, Engine Oil Temp, Trans Oil Temp, Fuel Inj Control Module Voltage
Boost, Batt voltage, High Pressure Oil Pump pressure, Injection Pressure Regulator duty cycle
Charging: Requires a 90 degree Micro-USB cord that will tuck in behind the tablet, plugged into a 12v USB charger wired in back inside the dash (or wherever) You want a 3A charger...or the tablet will go dead w/ extended use of several hours. Like these or similar.
For me, this gives me everything I could want. I'm sure there are many more possibilities. Like I said, I've just scratched the surface.