I checked the posts on the rear spring rubbers and tried to find them at gmpartsdirect but I couldn't access any pictures or drawings to confirm the right parts. Is gmparts direct a reliable source or should I head over to the local chevy store?

Also, I noticed my 87 firebird shop manual doesn't list any bolt measurements, will the parts desk know how to order replacement suspension bolts?

 

IIRC, the rear isolators are really no longer available. Apparently, the ones that can be ordered are for 4th gen cars, and as a consequence jack the rear end up to an unacceptable height. I've ordered from GMPartsDirect. They are cheaper, but shipping is exorbitant (though the totat cost is still probably cheaper than your dealership). The counter man, if he's worth is salt, should be able to find what you need.

JamesC