Forgot some other stuff.
You'll need to unbolt an arm from the knuckle(everyone calls it a spindle).
Then the 69-72 brkt is a bolt on deal.
BUT, the original factory 4" wheels may not clear the new brackets.
At lest mine didnt, but they wernt original to the car.
Some 14x6's will(i've been told), but dont know which codes will.
Later 14x7's and 15x7's will.

One more thing.
Unless you drive on dirty and/or gravel roads, toss the dust shields(backing plates).
The brake rotors stay cooler.
Learned that from Herb Adams( one of Pontiac's 1st gen engineer).