Best way to raise my Duster

I have a '74 Duster, and even with 14" wheels on the front and 15" wheels in the rear, the front is too high. The rear shackles are about 5", I'd like them to be twice that. So, what would be the best way to raise the rear? Just get longer shackles? Different leaf springs? New shocks? (I haven't really looked into the shocks, if they are air shocks or what; could they be worn out and that's why it's so low?)

It is not a daily driver; just used for shows here and there. I just need the correct 'rake' for it.

Thanks for helping out someone who doesn't have all the technical knowledge!