KB I am getting confused with your statements. If it has no mag it is neither a stagger feed nor a centerfeed it is a single shot action.If that is the case then in all probability it will take just about any small shank barrel made to be used with the .473 bolt head if you do not want to change out the bolt head,if you are willing to change then just about any caliber will work.
Now if it is a target action then I believe you need a large shank barrel but the same applies as to bolt heads.
Probably the easiest way to confirm what you have is to call Savage 1 800 370-0708 supply them with the serial number and they will tell you exactly what you have.