I pretty much agree with the other posters on getting skilled labor,
I've done it twice, perhaps more out of ignorance and bravado than
knowledge and skill. My method is: 2 pieces of 1/2" rod 1 1/2 - 3'
long, (rebar will work but not ideal). As you wind, the upper bar is
inserted as soon as the hole is available, and serves as the next
pull / safety. They have to be way tighter than you imagine, and it is
indeed dangerous should you; lose your grip, have a rod slip out, or
have the spring or any part of the assembly let go while you are
working on it. I have usually tightened it as much as I imagined it to
need, tightened the set screws, put down the tools and done a run
through. That gave me an idea just how much additional tension was
needed.