My spare rear spring is buried in my plastic garage that caved in from the snowstorm the other day, but here are some measurments of the spring spreader I made. Remember, it looks just like the one Tom Endy pictured, except I used 1" square tubing.
The 1" square tubing is 30" long with a 12" brace welded across the middle. Each threaded rod is 12" long and cut at an angle for welding to the steel plates. The steel plates measure 3" wide and 3 3/4" long with about another 3/8" stub left at the corners to lock into the sides of the spring. Notice how I ground the ends of the plate and stubs at an angle to fit the spring.
The 30" square tubing was heated red hot in the center and bent to a 30* angle. The 12" brace is cut at a steep angle on each end to fit against the 30" bent tubing. If I pull a string tight to the bottom of the ends of the bent 30" square tubing and measure up to the bottom of the 12" brace I get 2 3/8". The string measures 28" from one end to the other end of the bent tube.
The 12" threaded rods are cut at an angle and the steel plates are welded to them at a 27* angle. Installed in the square tubing, with the nuts all the way collapsed the end to end measurement is 38".
It took some time to measure and figure the angles to make sure the spring spreader would fit the installed spring, then collapse enough to be removed when off the car. Hope this is enough information so you can make one. If you need more information or pictures, just ask.