does a 72 cutlass have disc brakes and are they power? i want to change the rear to disc also will iu have to change the booster?

 

Well disc brakes are an option. You'll have to look to see if the car has them or not. Power was also an option. If the car has a booster then it has power brakes.

 

It does have a booster. I want rear disc brakes also

 

Well then I think you need to look at aftermarket brakes all the way around.

 

And most likely bigger wheels.... at least 15" from what I have seen...

 

From the factory, earlier 72 production was drum, all the later production is power disc brakes. The rear drums stayed as convential drum brakes until the 90's when all wheel disc and ABS came in.

If you're changing over your car from drums? Yes you'll need to change the proportioning valve. If you already have an 11" booster for disc brakes on the car, I don't know if it needs to be changed or not.
Gearheads78, 507OLDS or Joe Padevano could probably steer you in the right direction