Hi,
The 8 cylinder value is relevant to your real world tachometer, not the ingame representation.
The RevBurner can output RPM pulses to drive a real tachometer(or a speedometer with the right firmware). The more cylinders, the more pulses the tach needs.
Most aftermarket tachometers allow you to set the cylinder count to 4,6 or 8. Four requires the least pulse count, and should allow you to use the full range of the rev scale on your tach.
Should you choose to purchase a factory tachometer or dashboard, be sure to check all instruments are driven electronically. Older dashboard can have a mechanical speedometer, and a tach for the real world Lotus would most likely be mechanical as well.
You should also be aware of the cylinder count the tach/dashboard is built for. If you need 12K RPM you should opt for a 4 cylinder model if possible. Otherwise you will not be able to reach the end of the rev scale.
Another option is to change the gauge face of the instrument, if a tach goes up to 8000RPM stock, you could change the decal to read 12K in that position.
Most dashboards can be modified in this way, alternative gauge faces can be found on ebay or an aftermarket catalogue.