A friend wanted his 66 convertible hood springs bead blasted but he wanted the inner surface of the coils done as well. I made a spring stretcher to do this. I have thought about this for a long time and procrastinated. A couple of beers will get me in a creative mode.
Pic 1 - A three foot long 3/8-16 threaded rod and a 3/4 x 1/16 wall square tube for materials. Also are four 3/8-16 nuts and four 3/8 flat washers.
Pic 2 - The rod cut to two 6 inch long pieces, and the tube cut to two 5 inch long pieces.
Pic 3 - After marking where to drill two holes in each tube, 3/4 inch from each end, I drilled pilot holes.
Pic 4 - Then I drilled two 3/8 dia holes in tubes.
Pic 5 - Here's everything needed, the tubes, the rods, the nuts, the washers and the subject springs.
Pic 6 - Partially assembled. Note that to stretch the spring you need to thread one nut on each side to slide in the tube, then you can "stretch" the spring by wrenching the nuts to the ends.
Pic7 - It works.
The only change I would make is cutting the threaded rods at 7 inches, an inch longer. For reference, a un-sprung 64-66 hood hinge spring is 5 1/2 inches long. If your spring is longer, make the rods longer. It's not rocket science.
Jim