I'm having a bit of trouble following your question.
Are you trying to swap an idiot light cluster for one that has gauges? If so, you need to locate a gauge cluster from another El Camino or the Monte Carlo SS. You will also need what is called a "Tach Filter" which is the wire that takes the signal from your distributor to the tachometer. You want to make sure that the new tachometer came from an 8-cylinder engine. (I'm assuming you have a V-8 under the hood. If you don't then you need to find a 6-cylinder tach) The clusters pretty much plug & play. Just be patient while removing the old, etc.