Not providing legal advice, but then again, that activity is illegal under most state codes. Ohio as an quick example.
See section B.
(B) No person shall install or reinstall in any motor vehicle a counterfeit or nonfunctional air bag or any object intended to fulfill the function of an air bag other than an air bag that was designed in conformance with or that is regulated by federal motor vehicle safety standard number 208 for the make, model, and model year of the vehicle, knowing that the object is not in accordance with that standard.
Clyde is right, if the part to repair it back to the legal standard is not available, off the road it goes.
Let's not even get started with tort law assuming someone is injured because of a non functioning supplemental restraint system...
If you want to play design engineer at home, it makes a lot of sense to start with a chassis made prior to 1967.
Careful what you recommend Fellippe, those PE letters after your name come with a tremendous amount of public safety responsibility.
YMMV,
Erik