Bought a new Porsche Genuine airbox last winter when I rebuilt my '83 3.0. Didn't put a pop-off in as per Zimmerman. But I also was very meticulous about the CIS initial setup (
Dummies thread) and my engine popped right off (haha!) and hasn't backfired once since the rebuild, going on 8000 miles now. If it backfires and blows the box, I may just eat Ramen for a year and go EFI ITB.