I think there is supposed to be a metal sleeve that goes inside the lower bushing which allows you to tighten the body mount but prevents the rubber bushing from becoming too compressed.
Here is a pic and some links.
Here is a thread on replacing body mounts on a 67-72 truck. Should be similar to Blazer. Look at the PDFs. PDF 6, shows the original body mount being loosened, notice how it’s not compressed as much as how you have it. PDF 8, shows the lower bushing removed with the metal insert sleeve still in place.
http://67-72chevytrucks.com/vboard/s...ht=body+mounts
Wes sells a high quality rubber body mount set for Blazers. Post 64 shows the set with metal sleeves included.
https://67-72chevytrucks.com/vboard/...=721801&page=3
Do you still have the original body mount parts? Maybe you can reuse the sleeves.