I don't know why an 80's GP would be more prone to setting the Air filter on fire than 10's of Millions of other cars of other cars from that era. I would ditch the flame arrestor and put in an airfilter. It has to be a restriction and you already have a very limited amount of HP to work with.
If a car backfires, fix the backfire problem. A flame arrestor is something a Hack at GM came up to band-aid a problem another hack gave him 40 years ago, because crap rolls downhill. Break the rolling crap cycle.
