Weird. Finding a deep offset box end wrench is almost impossible. But in the States at least, you can get strut removal kits for about $25US. Pretty easy.

The problem with holding the center shaft is that there is the top shock seal to worry about. If you can get higher on the shaft than where it can bottom out inside the shock, then you're home free. But if you etch the center shaft, it's almost sure to spring a leak somewhere.

If you do it on the bench, it might be easier access-wise. Once you break the nut loose, put the spring compressor on and finish like that. But watch your face. I hate working around spring compressors.
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chris herbst, near chicago