On my 73 with the old style Gabriel Hijackers I have to take the floor jack and put it under the front spring eye and lift that side up to where the tire is almost off of the ground, then air up that side then do the same to the other side. I even have the Mr Gasket Shock extensions on top.
Maybe too, are your shocks the right length ?.
I also put a neat setup on my 68 called the Jac Pac 175 made by Delco. This setup does raise the car some but I mostly put it in for keeping the car level and being able to adjust things with the trunk full or empty.