Here is a trick for installing almost any tension spring. This is particularly of interst to those that have ever tried to install the "Godzilla Spring" on a C1 clutch. Take the spring and clamp one end in a vise and bend the spring to the side. and install a washer in the gap. Bend the sring the other way and insert a washer in that side. Just keep doing that until you have extended the spring enough to install it. After it is installed, just close the lid, and the washers will just fall out and you are done!
You can do the same thing by hooking one end of the spring to the axle on a floor jack and the other end to the lifting plate, pump up the jack to the dimension you need, stuff washers or wooden shims inbetween the coils, then remove it, install it, close the lid, and clean up the stuff that falls out.