Bear posted this earlier link for a '69 & the steps are near identical for a '70-72 dash OR or a 2nd Gen Firebird dash.
To add to Bear's well written response, I would add:
-take time to carefully unbolt the under dash AC ducting, dont destroy it. Really nice condition plastic ducting is getting harder & harder to find. 25 years ago, that's the type of parts many of us gave away.
-carefully remove the factory radio/stereo or aftermarket stereo. Oem radios/stereos had a small stamped steel bracket that mounts off the rh back side of the radio & stretches down to the bottom of the dash structure where it attached with a small bolt that comes up from the bottom.
-I've found it best to start from the passenger side, removing glovebox door, glove box liner, working to the driver side, & eventually, the stamped steel "speed nuts" above the glove box area, holding the molded dash to the rh side if the metal structure of the dash. Doesn't hurt to have an extra set of hands when it's time to carefully slide he molded dash back towards ones body.
-As Bear mentions, it's a lot easier with the front bucket seats or bench removed. I would also add to that, take time & remove the console & auto shifter, if car is so equipped. One of the most exasperating experiences ive had pulling these molded dashes was on a dash asm i learned a costly mistake on. This was decades ago, the result was slightly chipping the leading edge of the dash asm when the dash rolled into my lap as I kneeled on the floor. The part sticking up was the auto shifter w/o the shifter handle. Ever since that day, I've always removed the floor shifter when removing or installing nice dash assemblys.