I put a 79 dash in my 78. That is the same as what you want to do.
Basically everything is the same ,layout wise.
You will need to change some things.
1. the center outlet duct that bolt to the heater box.
2. the cluster is the same, but the clear plastic is different. The turn signels
are in a differetn spot.
3. the wiper switch is different
4. the clips that hold the dash to the metal part are different
5. you will need a plate that is riveted to the dash of a 79-up dash.
(I have a templete if you need it. It's only a flat peice of metal.)
The lower dash plastic on the 79-up is the same for the 70-78 dash, you can re-use yours if needed.