You should be asking any aftermarket Air suspension related questions at baggedbirds.com ...
The shockwave can replace a spring / shock combo .. its a direct bolt on for certain types of suspensions like Mustang 2, or may require a new control arm to bolt onto a different vehicle. Its used to replace a point in the suspension that needs a centralized stabalizing point .. if you were simply replacing a spring alone, you could use any conventional airspring since the shock is seperate.
On the Thunderbird, it would be necessary to make brackets to use the shockwave on the front suspension. There are a couple available, the SIC Motorsports has machined billet aluminum brackets on a shockwave with the adjustment knob on the very top and comes with spacers so you could adjust your lowest drop point, cost is $1075 plus shipping which is well worth it, considering the shockwave unit by itself is about $800. They use the one for the newer mustangs, which is a bolt on kit from Air Ride Technologies, but wont work on the Tbird without different brackets.