The Chevelle is 40 years old ... and most likely ... the original springs have already " LOWERED "
themselves a inch ... maybe more. I have a friend who bought some 2 inch lowering springs and he got about 1/2 to 3/4 of a inch results ... because the springs on his 66 SS Chevelle had settled a decent amount over the years.
That is why you should always change springs in pairs
I see no real issues lowering the car a inch or two. Any more and you can run into driveshaft interference with the bottom of the car.