You cant get arround the SCORE thing. You`d have to make a whole new entry in the game source for that.
I suggest you use the OverlordTankDraw (naming correct?) module and attach you turrets using the overlord upgrade modules (eg. Purchase Upgrade and Get Vulcan Cannon and a sidebar change, purchase different upgrade and get RPG cannon and sidebar change, etc.)
The sidebar change is mainly of cosmetic value
