I have Air shocks on my 68, in order to have the rear up where I want it I have to add a lot of air. This makes the ride very stiff and will hop over washboard while cornering or going up-hill. I'll be replacing mine with standard shocks when I get new springs, for a better ride and it's easier on the upper shock mount. Trouble is getting the spring you want, Eaton has five stock height springs for a 68 coupe and more for a vert, they also offer +/- 3"in height for each of those load and spring rate springs. It's a lot of work to replace the springs and then remove them again when you find the new springs don't give you the ride you want, I had my front coils in and out four times. A lot of others offer spring packages but as stated most are going for the low stance look and lowering springs are the norm now. I kind of like the classic muscle car look with the rear a little higher than the front with the rear tires a little wider than the front as well. Low riders with large diameter wheels and low profile tires not so much, unless it's a 63 Impala.
But that's just me, each to his/her own.