v/6 tach in a v/8 monza

[my79monza]

I just bought a complete instrument cluster from a monza spyder to install in my base model.
It came from a v/6, I can use the appropriate sensors to make the gauges work but what about the tach?
I know to convert a 4cyl tach you use a couple of resistors to use with a v/8.
What do you do in case of a v/6 tach to convert it to a v/8?
Thanks, Merle

[monzaaddict]

unless it is a 75 with the gt vega type dash, the tach will have a switch on the back that is adjusted for any engine.