where to mount shackle hanger braket

[rollenhard]

I bought a 50 Chevy truck with a 1986 chevy camaro rear end and leaf springs nothing was bolted up yet. So what im asking how do i measure the leaf springs to determine where to mount the rear shackle bracket? Look at the picture do i mount it at the No Tension On Spring red line? Or with Tension On Spring yellow line meaning i jacked up the spring till the lower spring pancaked to the other spring. Hope that made sense
Thanks