the instructions are included in the kit. i have an aftermarket one sitting around somewhere. it has three or four wires i believe. power, ground, one that goes to the engine somewhere. it'll also have a switch for 4,6 or 8 cylinders. mine never got installed as i got rid of the vehicle and all the other ones i had came with a tach.
as for swapping instrument clusters idk what that entails but i am sure others on here have done it.