I put a jack under the spring, You might be able to insert a spring compressor in there. I don't have the same suspension design on the wagon, so I don't know. There was an old style (rwd) coil spring compressor that fits in the hole in the center of the spring, then you swing the arms out to grab the spring, and clamp down on it. IIRC. people have had issues using that tool, but I haven't tried it myself.
What I meant by mitigating the leftover spring tension was by having an assistant use a long 2x4 under the control blade or spring seat to put pressure on it, so that when you loosen the bolt it won't jump off there. There will still be about 50-100 psi left on the spring. Someone with a 2x4 should be able to prevent it from separating violently. If you can't do that, then you should at least wrap a rope around the spring and the control arm, and tie those up somewhere on the body to limit movement.
IMO, it's going to be hard to remove the control arm bolt without something taking tension off the spring. Those things tend to bind up. If you can, use a spring compressor, remove the spring, then remove the control arm.
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Originally Posted by the user formerly known as ZX3_Chick
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