The Israelis went the other way and used a pair of 20mm Hispano-Suiza 404 20mm cannon on the quad fifty mount, usually fitted on former US halftracks or ex-Egyptian BTR-152 armored cars helpfully donated to the Israelis during the 1956 and 1967 wars. The Israelis very much wanted any rounds that impacted a hostile aircraft to be explosive ones, doubly so on helicopters, and considered nighttime attacks on supply, fuel and ammunition supply columns to be the most considerable threat from above at the time the guns and their obsolete vehicles remained in service.
The late Mike Dillon had an M16 halftrack mount for a quad fifty retrofitted with an M134 minigun. Just think if he'd tacked on a pair, running one at a time, so that the second could let fly once the first had been emptied and was reloading....
Or four M134s, one in each of all four gun positions, if you want to be really promiscuous about it.
But there are other possibilities....
