As mentioned, have a new rubber boot ready as the old one is probably shredded. My bumper stops were fine and I reused them. They seem pretty sturdy so you may not need new ones, but then again you don't want to do this again. I did this once with worn shocks and the pistons were easily compressed and held so you had plenty of time to slip in the new mount and boot. I later replaced the shocks with new Bilsteins and then later had to change one of the mounts again. Compressing and holding the piston on a new shock is a lot tougher. You might try tying it with some rope. I controlled the spring by resting the weight of the car on stands under the LCA.

glenmore
1991 300CE
2000 C280