Rear springs can be interchanged 1979 to current on panthers. To use coil springs in favor of the air springs it's just a matter of obtaining a pair of springs and a pair of spring isolators (D9AZ-5536-A x2)
Ford slightly increased the static ride height for 03+ CV/GMQ springs but kept the rate the same (130lbs/in for non-CVPIs - CVPI coils are 160lbs/in)
So, you can order the current production CV/GMQ base springs from Ford and keep the ride height a little higher - but with the softer spring rate rather than going to the taller, but noticeably stiffer CVPI/TAXI coils.
New rear springs from Ford are cheap, normally ~$60 a pair if you shop right.
Aftermarket springs can be used, but note the ride height may vary as they are more of a universal fit for all '79+
Ford typically supercedes the previous spring part numbers with the current product as they interchange anyway.
Whats wrong with your rear air suspension anyway? As long as the issues aren't too extensive, I'd just repair it as I find the load leveling function very convenient and on the customization aspect that the ride height is infinitely adjustable to your preference by adjusting the sensor