I like the idea of using the stock dash. To me, the speedo and tach locations recessed in the stock dash with the "hoods" over them are very similar to the large fender flares you have on your car, I think that they compliment each other and tie the exterior and interior together nicely. I've always like your car because of its beautiful flowing body lines and I think that something similar on the interior is fitting.
Most of the custom dashes I see in Z cars make the car look cheap and unfinished, the exceptions being the 240SX dash, and the ferrari GTO dash (on GTO replicas of course) If your going for the all out race car look, and this will be a track only car a super lightweight dash with a stack data center would be ideal. But if you plan on driving it on the street and cruising around (and I hope you do!) It might be more comfortable and appealing in the long run to have a stock, or lightly modified stock dash in place to help make the car feel and appear finished and road worthy.
There is a company in Australia and recovers dashes, they also do custom modifications on stock dashes. You could add one or two more gauges pods to the stock dash, or slightly rework the stock dash to accept gauges or switches or your choice, then ship it to them to have it recovered. That might be something to consider.
Glad to see that your plugging away on getting the car up and going, if you ever find yourself on a test drive up in SA drop me a line, I would love to see it!