If you plan on having the springs replaced on your 1970 Buick Skylark that would be the ideal time to also install the Air Lift AirLift 1000 Drag Bags # AL60844. It can be possible to install these air bags with the spring still in the car, but I would be MUCH easier to do it with the coils off of the car.
I have installed these in a couple vehicles now and ended up taking the coils out to make the job easier. Trying to install them with the coils still in the car can be pretty difficult.
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The best solution for your 1972 Buick Sylark would a universal base plate kit like the part# BX88230. This will bolt to your bumper. Most bumpers will need to be reinforced or modified. Brackets must mount to a flat, metal surface.
I attached some help articles on flat towing for you to check out as well. view full answer...