The first-gen instrument panel (IP) stretches as one piece of plastic across the whole dash. Starting from the left, there's a vent, three circular guage insets, then the Command Center (idiot lights on top of the climate controls), and then another vent. I'm assuming that since you are prepared to match wires, resistance, etc. for digital guages, you're also prepared to customize the dash plastic. I recommend not mucking with the vents, the climate control, or the Command Center feedback lights, so that leaves the three stock guages, which are about 4. 75" in diameter, and separated by 3/8" of plastic trim.
Based on your 14" x 3" estimate, I think you'll have plenty of room to do what you want (depth should be fine, too, there's a lot of space available behind the dash). Fit, finish, and trim seems like the biggest obstacle, here. On my '93, all the instruments (including the odometer and speedo) are analog display with a digital signal. You should be able to match up the various resistance and current signals from the stock senders to provide signal to your aftermarket display... hot-rodders have been doing similar things for years.
Post up pix here if you do this... sounds interesting.
Randii