Hi,
I believe the GM part number is 20829013. They refer to it as an insulator.
As far as replacement, you need to first remove the torsion bars. They are under tension. Once they are removed, unbolt one side at a time to remove the bolt from the cross member. If you can't, remove the old bushing and install the new one. However, you may need a press to remove it and install the new one.
If you look below, I attached the directions for torsion bar replacement. You aren't replacing them, but this is the only way I have the directions for removal/installation. I highlighted the bushings in the pics. Also, you will need to rent a special tool. See directions starting with pic 2. Pic 1 shows part.
Let me know if this helps or if you have other questions.
Take care,
Joe
See pics below.
Images (Click to make bigger)
Monday, February 7th, 2022 AT 9:33 PM