It can be done, I know: I did the swap...
I have a '92 100NX, with a GA16DS in it.
Bought a Digital Dash off of eBay for $35,-
spent half a year researching and then 4 weekends on rewiring.
I actually made a second set of plugs for the Digital Dash,
so between weekends I could put the analog one back in
and drive my car as it is my primary vehicle.
The Fuel Gauge is accurate, I have to replace my Temp-sender
with a newer one with a slightly different curve.
The Speedo-Cable was replaced with a sensor off of a Sunny N14.
It swaps right into place where the cable-drive used to be.
The Tach required a custom piece of electronics which I built myself.
This was the hardest; I am now on my 4th revision and it FINALLY
works like it should...
On the GA16DE-equipped cars the ECU has an output for the tach,
which gives pulses to ground. The dash has an internal "Pull-up".
The Carbureted engines (DS) splice into the coil-wire so are
12V with a "Dip" to ground and then a spike causing the pulse
in the primary ignition coil. I Made a converter that takes this
"dip" and converts it into a nice short to ground for the dash.
If you need a wiring-diagram for the dash; I have one on-line
for a week or two. Right-click here:
DigitalDash-Connections.pdf
Drop me an email and I'll try and aswer more questions,
I don't check out here that often...