The '88 bolts you're looking for are metric, 12mm in dia, have a pitch of 1.75, are 95mm long, and are grade 10.9.
In short, they are M12 x 1.75 x 95 (10.9)
On the '84-'87 cars, the forward lower control arm bolt is almost the same except that it's 90 mm long. The aft control arm bolt on these early cars isn't the same at all. You may be able to get away using the forward ones but just be sure you have at least a thread or two sticking out beyond the nut once it's fully tightened because the locking feature on the nut requires that the bolt pass completely through it.
The stock system was designed with rubber to give a certain level of compliance to the bushings which the Pontiac engineers felt would be a good compromise between handling, road noise, and cost. I prefer stiffer bushings and the (marginally) greater accuracy and quickness they provide to steering response, so I use polyurethane. To each his own though.