Coil springs are not that complex. Either the springs are wrong to start with, or someone cut/modified them, or the spring mounting is messed up.

Did the previous owner cut the current coil springs? Lots of guys will hack off a coil or two (or more) in an attempt to lower the car. New coil springs are not that expensive, you should be able to buy them longer or stiffer then what you have now. You will want to talk with a good spring guy, then buy from him.

It also may be easier to correct a spring mounting issue then it could be to try to cobble something to make it work. Pictures of the springs/mounting brackets would help. Gene