Raising Rear End with a Lift Block kit on my Slant six

I wouldn't use shackles to try and raise the car. They will be temporary at best, because what they will do is cause the spring to arch backwards and bend more and possibly even break. shackles are not to raise the car. their only purpose is to lower the rear spring attaching point when using springs with an arch so great that you cannot use the stock location any longer. Most everybody uses shackles incorrectly. they can become dangerous because they allow the spring to put more lateral leverage on the hangers and possibly break them. Air shocks are probably your best low cost bet, or maybe some kinda helper spring. The most correct way would be to just buy new leaf springs.