Replacing suspension parts is not a restoration. Restoration suggests making like new again. Perhaps the proposed work is better described as a rebuilding with modifications. Not to dissuade you from doing anything you please, but if air bags are being considered, why not adapt a suspension from a newer model, along with the newer model's drive train?
One could argue that the manufacturer once "toyed" with an air suspension on the E3 "
Nivomat." It would be interesting to know how many of these systems are still using the nivomat shocks, or for that matter, whether they are currently available. These were not compatible with the E9, although I have heard of at least one attempt to retrofit them. That same experiment morphed into a set of aftermarket rear adjustable air shocks where the height could be controlled by adding air pressure to a shared schrader valve hidden in the trunk. In other words, there was little, if any, additional plumbing and hardware, i.e., compressor, tank and wiring to the compressor.
Additional considerations include the longevity of the typical air bag system. I dare say, they probably do not equal the typical lifespan of the stock suspension or other traditional (stock-like) aftermarket suspension parts, e.g., Bilsteins or Konis. One modification worth considering that is comparable or superior to the traditional suspension setup, would be coil over shocks, which provide some of the best of both worlds, including adjustability (height and damping) and weight reduction.
It is unclear whether each suspension corner using an airbag is independently controlled or whether it is merely the front versus the rear. If one corner develops a leak, leveling the suspension could become problematic. And, if one bag goes bad, would that necessarily require replacement of the other bag on the same axle?
Another consideration is what stock parts, e.g., spring perches, are "permanently" removed with the installation of an air bag suspension, and for that matter, what parts are permanently added for the air bags. I suppose all modifications are reversible if you don't mind re-engineering the chassis and undertaking some metal work, but some modifications are easier to reverse than others. This could pose an issue for any potential sale to someone seeking "stock" or stock "with acceptable upgrades."
While I have nothing against air bag suspensions, air bags were the source of significant frustration for a few former Lincoln owners, after suspensions developed issues out of warranty. Riding like a Cadillac may not be what you are after either. A "boulevard" ride is one thing, but Fleetwoods, Broughams, Coupe De Villes and Eldorados hardly conjure thoughts of taught, crisp and responsive handling. But there is something to be said for a wide bench seat if you feel like a nap.
