They are 52 mm. Good job on the Google effort. It is possible you could make a larger one fit since it's just an opening in the dash. But you'll have to figure out the mounting for them and the finish hats won't fit on top.
There are plenty of brands other than Defi. I've seen guys with completely customized programming that would display just about anything they could get a sensor for. They can even tap into the OBDII for your data.
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2011 370Z 6MT Sport Gun Metallic | ARC | CJM | Ecutek | FI | Fujimura | R2C | SPL | Stillen | TWM | Z1 | ZSpeed | |