Front springs was my immediate thought.If they check out to be the same springs on both sides, loosen the spring eye bolts, put it on the ground, bounce it a few times and see how it sits. If its level, tighten things up with the weight of the car on the springs. U can do this with jack stands under the axles so you can fit under the car.
Bingo! Chain around spring to frame, slowly lower the lower control arm with a jack while the frame is on stands. 99% of the tension will be off once the arm is all the way down, then just pry the spring out.Thats really bad advice on so many levels. Threaded rod or all thread should never be used to compress a spring, spring compressors use hardened fine thread rods that are HEAT treated along with hardened washers and bearing material. All thread that hardware stores sell might have a color grade (if your lucky) but is not hardened, not suitable for this type of work. Your nuts are grade 5 probably from Loews. They rent spring compressors for FREE at the Auto parts stores! The shock tower was not designed to take that load directly. And if you cant afford a free spring compressor rental you can use the weight of the car to unload the spring as long as you wrap a chain around one coil and anchor it to the frame to keep it from killing somebody if you do it wrong.
I purchased one like that to use on my Fox body mustang ( except it was over $200) and it was very well made.. Unfortunately the discs would not slip between the coils so I could not use it..The best and safest coil spring compressor that I have found. Used it on my wife’s 84 Z28. Worked like a champ. Bought it on E-Bay. The more you tighten it the more surface contact you have on the coil of the spring. Made for Mercedes Benz but worked great on our Z28.