The case you are describing, is a standard AT noname case from the mid-90's. They were common cases back then.
The thing about the LED display, is that they are usually customize-able using jumpers.
To set the digits, you need to do it with power on, if you have no manual at hand. (they can survive doing it with power on)
The led's are soldered onto a PCB, and the jumpers are on the back of that PCB.
Regarding the turbo-button wire. Well... I have only seen one case with three wires, all other that I have seen since the
late 80's have all been with two wires.

Well all the AT cases that I've seen with LED displays (not that many actually) had 3 wires, but that's not gonna change anything : three wire turbo button can do the exact same job as a two wire button ; just plug two of the three pins and it should be good (the middle pin is usualy the common wire, and then if the button is in normal state, one site gets on, and when you press on it, it gets off and the other side gets on. As simple as that)

Deksor is right. The type of display you are looking for has 3 wires (in this example white/black/red)
but only 2 of them are actually connected to the motherboard. Which two wires have to be connected depends on how the turbo function is activated via the front panel button.

Connecting the turbo button wires to the motherboard is easy, just load up norton sysinfo, select cpu speed and connect the wires. Then you can normally choose if button pressed in, are turbo activated, or the turbo button pressed in are machine-slowdown.

The point of a fully wired 3-wire button system is to enable easy connection in all possible scenario's - thus with motherboards that have either turbo mode on with shorted turbo header -or- turbo on with open turbo header -and- to enable synchronicity with the turbo led on the front panel whether it is connected to the motherboard or to the display. A 3-wire turbo button with all 6 wires attached can handle all possible scenario's without the need of soldering or de-soldering - you only have to ignore 1 wire to make it work.