BUG (not possible to fix i guess): no fire & firearms for minigun. Tampa3 needs to be spawned and be in the near of Centenario to work on it OR attach it with MENYOO and make invisible (and invincible). 
You can also use included 'LP770 LSPD (Add-on).xml' and drop it to: 
GTA 5\menyooStuff\Spooner and load the file with Object spooner of the Menyoo Trainer in game. 