My take for suspension would be a call to Phil and Jeremy at the Roaster Shop, order up one of the RS Fast Track chassis or their new REVO chassis!!!! You won't be disappointed. I know you are going to say its out of your budget but I world give them a call first, I bet you will see when you start to add up all the parts and labor to redo your 44 year old frame it's not that much more??? Then see what all your options are?
http://roadstershop.com/chassis/chevelle-chassis/
They do not show REVO for your car but I'm sure they could build one for you??
Give them a call great car guys that get it!!