Here is an email I just received from the guy who put the SPA gauges in the RX7:
I have some newer SPA displays that I need to install, to fix the
"display goes black when it gets too hot" issue that the old units had
(the units with switchable red/green illumination are the newer style
and are supposed to be more tolerant of heat). I am looking at one now.
The gauge cup itself is relatively shallow at about 11/16" from the
gauge face (with bezel and glass removed, and the protruding lip on the
cup cut off) to the back of the cup. There are some screws that hold the
electronics to the cup that add about 1/8" to that depth, but they have
a lock washer that could be removed and perhaps some lower profile
screws could be used if there is a clearance problem in that area. You
could even just glue the electronics in the cup to eliminate the screws
completely if you had to. The main clearance problem is for the
connector on the back of the gauge, which sticks out 1/4". For my RX-7
install, I cut the plastic part of the connector down and soldered some
wires to the connector pins and then used a separate connector at the
end of the wires to connect to the sensor+switch wiring harness. I
suppose you could also cut the connector off below the back surface of
the cup and use some small gauge wires and route them out the side of
the cup for minimum depth. You could even eliminate the cup, I suppose.
But you could do 7/8" without going too extreme, 11/16" routing the
wires out the side of the cup, or perhaps even a little more shallow
(9/16"?) by eliminating the cup completely. If it's close and you'd like
some more precise measurements, let me know and I will pull one of my
new SPA gauges apart (since I will be doing that anyway) to measure it
better.
If the depth isn't too much of a problem, the NSX cluster looks like it
would be easier to install the gauges in than the RX-7 cluster, since it
has some round indentations already in place for the stock gauges.
You'll need to find a spot for the little push-button switches, too, but
I am sure that won't be a problem.