They are a unibody.
Have you contacted Air ride technologies to see if they offer a kit? The same upper and lower control arms fit 68' to 73' and the coil spriongs for 67' to 73' are interchangeable. The only difference I can see is the upper shock mount. The Air ride kits replace the coil spring and shock with their airbag. So, if they offer a set up that uses the 71' to 73' upper shock mount then you're covered. If not it should not be to difficult to fab a mount for the top of their set up.