I'd argue AA guns aren't obsolete. Perhaps even less so today with the threat of drone storms. If you have to fight off one hundred drones at close range guns make a lot more sense then missiles. You're starting to see a resurgence in AA guns with the Germans coming up with a rather neat integrated stationary AA gun system intended for protecting major targets like airports/airfields.
en.wikipedia.org
It's an interesting system composed of six networked 35mm AA guns connected to radars and fully automated.
Even today the Russians continue to combine guns and missiles for most of their SPAAG designs.
For the short term in the 80's I kind of like the idea of the US licensing the Gepard system and mating it with M1 or M60 hulls. Then see if you can attach a few Stinger MANPADs to it for added oomph. Maybe eventually go for a Avenger looking like system with one of the 35mm gun "Arms" replaced by a multi shot Stinger box launcher. Or potentially a "Tunguska" like design with a couple of two tube Stingers attached to each side of the SPAAG.