The dash harness would have varied because they added the seat belt light in the later years. The harness is probably expensive too.
Besides the Rally gauges, you need the light bar and switch panel. Then there is the panel below the switch panel that will have to be swapped out for your heater controls.
As far as wiring goes, you can modify your harness to make it work. You need to add a constant power wire for the clock, and a switched power wire for the tach. Then you need to run a wire from the "-" side of the ignition coil for the signal to the tach. You might need to lengthen some other wires, but that's minor.