Master Model 1/72 M197 Three-barrelled rotary 20mm cannon - AM72038
M197 - Three-barrelled rotary 20mm cannon - turned barrels with etched barrel clamps - used on AH-1 Cobra.
It is very simple to use in Your model, and makes it extremely realistic. Insert the metal parts using Cyanoacrylate adhesives. Drill proper hole in plastic part if needed.