used 3/8 in. thick by 5.5 in. by 3 in. cold rolled steel, its just a bit too thick so grinding some thickness off along the path of spring contact , just a smidge, was necessary, its OK, worked

3/4 in X 10 thread per inch rod

normal nut on bottom

coulpling nut above to engage more thread on the active end

it did compress the spring enough to lift it off that spring seat / plate

now the lower ball joint is stuck

previously, cleaning the control arm to remove insulating grime, where the ball joint needs to break lose, and propane torch heat plus that harbor freight seperator you pictured the the thread:
http://www.peachparts.com/shopforum/diesel-discussion/323469-lower-ball-joint-separator-w123.html

has worked, not so far though