IMO...all you need is some threaded rod of the right dia. and length, some large washers, and the correct size nuts...
remove the shock place the rod where the shock went, install the washers and nuts on each end and tighten it up a bit then unbolt your upper control arm and slowly loosen the top nut until the spring is no longer putting tension on the threaded rod...and your done...the rod should be about three feet long or longer if you want to be really safe. You may want to double nut the bottom nut so you have a place to hold on to as you loosen the top nut to release the spring tension..
should be fairly cheap to make
Just my 1 cents worth
BTW The threaded MUST be more than long enough to COMPLETELY release the tension on the spring WITHOUT running out of thread...
I made one similar to that several years ago. Mine bolts to the lower perch and has a large washer that engages upper spring plate, allowing me to remove the spring in the compressed position. This one appears to compress the spring in the car, meaning if you are merely changing springs you may have to remove the upper arm.
Once you get into the seriously stiff road racing springs you don't need a spring compresser. They are short enough to slap right in.
I had one of those. The threaded rod was not the greatest quality and stripped out after about 10 uses. I have been meaning to find a higher quality rod to fix it. It did work quite well though. Now I just run over to the local autozone for the loaner internal spring compressor they have. Freebie!