After verifying that everything is hooked up properly, dist/rotor are clean of contaminants and corrosion, the plugs are clean and adjusted, and fuel flow/pressure is within spec, it does sound like something was damaged during the backfire, most likely something in the AFM. I think I would search for a used AFM. Should be a bunch out there.
89 Milano (wife's daily driver since 1989, Shankle Sport)
91 164S (my daily driver since 1994)
94 164LS (~Q) (trip Alfa since 2000)
72 Morgan 27 (water time since 1976)
previously owned since 1964:
62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6