Raising rear ride height.

So I finally got around to putting my keystones on my car and have a problem with the rear ride height and was wondering how I would go about raising it. I replaced the shocks like 4 years ago but the coil springs are the originals. The tires on the rear are 255/60/15 and the lip of the quarter is sitting like 1/2 inch above the sidewall but if you push down on the trunk it goes right into the sidewalls. I'm assuming my coil springs are shot cause they're so old but I don't really know what kind to get. Do they make heavy duty springs or would big block springs make a difference? I kind of want to raise it an inch or two cause I need new tires on the back plus they're 60s and the fronts are 75s. Which also has me wondering whats the biggest rear tire you can fit on a stock 70 chevelle. Thanks.

Stock wheels


15x4 keystones 215/75/15


Kind of how I want it to sit These rears are 255/60/15