Removing those ball joint rivets on my 96 regal was one of the most frustrating jobs ever. The rivets were pressed in so tight that after drilling and grinding the heats off the rivets still would not come out. Had to center drill every rivet with a 1/8 bit before they would come out with a punch.
The replacement ball joints came with 6mm x 1.0 that were way too loose for the ball joints so replaced them with ΒΌ inch fine thread garde-8.