I also have a 70 burb, also live in Phoenix and in pretty much the same all around boat you are
I am going to go with the Vintage air in dash setup as I run it on my 72 truck, yep gonna cut the holes in the dash for the 3 vents.
Then I am gonna ALSO run the rear roof AC setup with a seperate fan control so I can set the fan speed as needed.
However instead of the original roof tunnel I am gonna use a later model cover as I have seen others do this and it works well & looks good.
All I am waiting on is a Good Guys Show special next weekend or a Black Friday deal after Thanksgiving to buy my Vintage Air stuff.
Lastly Vintage Air makes a larger condensor that I plan to fit into my rad support as we need all the help we can get here in the Valley of the Inferno.
Oh and anytime you want to hit the trail with me & another board member who runs a 72 burb just pm we...or check my build thread for info on how mine has come along.