Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
You will have to take the lower engine mount spacer out to replace the belt. When you get the nut off then you can take the stud out, then loosen the other nuts and pry the spacer out. Here are the steps from the manual.
REMOVAL PROCEDURE The accessory drive belt controls all engine-mounted accessories. All driven accessories rigidly mount to the engine. A spring-loaded belt tensioner maintains the drive belt tension. A belt squeak, occurring when starting or stopping the engine, it has not effect on belt durability. The drive belt tensioner can control the belt tension over a broad range of belt length. However, there are limits to the tensioner's compensation ability. When using the tensioner outside of its operating range, poor tension control and/or damage to the tensioner may occur.Remove the following components. Refer to Engine Mount Replacement
Install the belt. Refer to Engine Mount Replacement in order to install the following components:
Jack the engine up.
The motor mount bracket on the Buick is different than the illustrations on the answer. I believe the proceedure is the same though. Where do I place the floor jack to support the weight of the engine without damaging any parts?
Thank you for the quick response,