Well, depends on what kinda car u r working on.
A body 70-up, not gonna happen. Need a new (rally) dash frame to install rally gauges
E body - same dash frame, just need the gauges, headlite, wiper ctrl panel,light bar, heater ctrl panel, and i think the radio plate IIRC.
B-Body have no friggin idea, Im sure others will chime in
** not to mention the dash harnesses are different, as rallye dashes have gauges and reg dashes usually have idiot lites. But again, depends on the car/model. On an E, u can use the same harness, just need to run a wire for the tach, and switch out the oil sending unit for one w/gauges and i think thats it.