Just did the same thing a month back or so. You can use a standard harness with a few modifications. You will have add a tach feed and a tach power wire to the harness. These are available repro if you want. I bought the wire from the fuzz block to the coil repro. Since the rally dash has a clock, you will need to add a power to the clock. The oil pressure wire will have to modified as well since the rally has a gauge and the non-rally is an idiot light.
The bezel under the gauges with a non-rally dash has a moon shape molded into it whereas the rally bezel is straight across. I bought a piece of black abs plastic off of ebay and chemically welded it to the bezel. Redid the wrinkle finish with wrinkle finish paint and it looks awesome. About 20 bucks. In order to weld the plastic chemically, just dissolve some black plastic in acetone until it is a glue like consistency then just "glue" it in. You can use a little extra and sand it down to prep it for paint.
Rod