I emailed air lift and they got back to me with this info:
I'm sorry, but we do not have a product for the '67-'72 Chevy pickup with coil springs. There is no access hole in the upper or lower spring seat for the air valve and air line to pass through. There are large coil spring retaining bolts there.
I also sent them an email awhile ago asking about which bags to use with these same springs installed in a 1996 Wagon and they said they couldn't recommend anything for that application.