Repair-It

Well... Here is a cool Raspberry Pi application. You can use the OBD port with a Bluetooth adapter to send the OBD info to a Raspberry Pi. There are some options for receiving the signal and displaying the data to a screen. Here is a full solution:
https://www.youtube.com/watch?v=pSUUu_lPt0k
www.carberry.it


Here is a more do it yourself solution:
http://www.cowfishstudios.com/blog/obd- ... -head-unit
This has you buy a Bluetooth OBD adapter and a Bluetooth receiver for the Pi.
Note: in this video, it shows a double DIN aftermarket radio, with a video in. You can actually use any display and mount that display anywhere.

This could be a cheaper/cooler/nerdier approach.

Not sure what you had in mind for applications but I will say you should watch the Tom's Turbo Garage playlist on the LS Miata swap (and the 87 GN is also good). He talks about using a Dakota Digital SGI-5 or something for conversion between one "gauge language" and another. The point is, products like this already exist to help bridge the gap between different generation/brand computers and gauge clusters, which was one of your concerns.

LS swaps. The ECU should have the OBD connection, and you could use this instead on connecting the gauges. Should be the same data right? You could put a display behind the gauge cutout in the dash and connect the pi to the display. The pi could be hidden in the dash between the OBD connection and the factory gauges.

I don't disagree, but the concept that adapting to the stock gauges in whatever you are LS swapping into is "hard to impossible" is still something I just don't believe. People talking about doing a complete gauge transplant. It's crazy. 99% of the time I think I would prefer the stock gauges, unless they provided no information at all. Like stock Fleetwood gauges. But in those, rather than hack the dash, people typically install the 3 gauge A pillar pod.

I absolutely don't disagree that you can adapt the original gauges to the new ECU. I also agree that in most applications that would be the preferred method, to maintain the factory look.

I just wanted to throw out a different idea. I know that you could use adapters and maintain the originals, I just think that it might be cool to also modify the gauges since most interiors of the 80's cars sucked anyway. I could potentially make my own backing cutout plate, and have this display behind it. My application is striving to look stock on the exterior (that is mainly what I like about the cars)with the exception of maybe a cowl hood, but the inside, I don't care. I might use racing buckets, etc, so digital custom gauges to me would be cool since I will have "made" them to work with the car.

There is always this:
http://www.racepak.com/Drag_Racing/Dash_Compare.php plus http://www.racepak.com/Components/OBDII.php