67 GMC BAG ?'S

I HAVE A 1967 GMC. IT HAS REAR LEAVES. WHAT DO I NEED TO DO TO THE REAR TO BAG IT? MOST 67-72 CHEVY/GMC'S HAVE REAR COILS, WOULD IT BE EASIER TO CONVERT IT TO COILS AND BAG IT? IF SO, THEN WHAT IS REQUIRED?