@Cyrus72, I did a ton of research on this topic for my garage queen. re-read what Andrew wrote in posts 6 and 12...here's my input...
OE rubber body cushions will crush, crack, dry rot, etc. over time and will need replacement in another 15 years or so - depending how the car is garaged/stored (in the dry Arizona heat, salt air and high humidity of Southern Florida, etc). Doing a search I'm sure you can find the threads with pics of misshaped, crushed, cracked OE body cushions removed.
there are different durometer hardness values for the various brands of poly body cushions. Energy suspension is the highest durometer (hardness). Prothane brand poly mounts have a durometer value in between the energy suspension and the OE rubber.
In this Summit link
here, are the listings for Energy Suspension, Summit's house brand, and Prothane kits for our car. If you choose poly, get black ones as they have graphite impregnated in them unlike the red ones. At SEMA, the Prothane rep noted they are not making the private label kit for the Summit brand.
I choose the Prothane kit 7-132-BL....a poly not as hard as NRG, black in color with cad-yellow plated washers & sleeves containing all bushings 1-7.
Note that the poly kits all include positions 1 thru 7. the OE rubber kit from Kirban's, OPG, Classic Industries, etc. are only positions 2-7. you have to separately purchase upper and lower for position 1 - the radiator core support bushings, from Kirban's. Ever notice how the vertical gap between the door and fender can get smaller as you get closer to the ground? Besides our Buicks not having the best panel alignment, the uneven vertical door gap can be caused by old, compressed radiator support bushings in position 1, causing the front clip to sag.
If you choose poly body mounts like the Prothane kit, I have to suggest the following....
do not use poly motor mounts or poly trans mount with poly body mounts. there is too much vibration transferred to the dash using all poly mounts. Keep things quiet and install new OE rubber motor mounts and trans mount when needed. MOOG has good choices, buy from Rock Auto.
At some point you may redo your suspension bushings - front upper and lower control arms and rear upper and lower control arms.
the best choice for a stock street car are the Moog Problem solver bushing kits in the front (MOOG K6411 & K6421) and MOOG K6178 for the rear (all, upper + lower).
Federal Mogul currently has an inventory control/quality control issue with the K6421 kits. I wrote about this back in December. Kit was coming with only one random bushing and not the 4 cad plated units for both front lowers, both sides. Federal Mogul pulled all inventory of this kit and has to schedule production at the Mexico production facility.
EDIT ADD>>>
check out this thread...
https://turbobuick.com/threads/should-i-ditch-my-poly-body-bushings-for-kirbans-rubber.438034/
you'll need new bolts for the mounts.
https://turbobuick.com/threads/need-info-on-body-bushing-bolt-sizes-etc.250953/