67 Barracuda project... narrowing 8 3/4 rearend

Hoping to get some opinions on best way forward with my 67 Barracuda project. The car was a Commando v8 4bbl car, now it is a 360cid Holley sniper EFI car. I am going resto mod with the car so am not concerned with oem parts but also don't want to wind up in a geometrical nightmare. I am looking to have a drivetrain and rear end capable of holding 650 crank HP. I currently have an 8 3/4 rear end with a 489 third member. I am trying to decide between rebuilding and narrowing the 8 3/4 or going with a 9" ford setup (also narrowed). I was thinking about going about 2 inch narrower (give me 1 inch on each side correct?) and installing the QA1 6 link rear suspension. What issues will I encounter with narrowing either, as far as fitment? Is it very technical to setup and fit the 9 inch into an A body mopar? (And what will I need to be considering for axle shafts, rotors etc? Thanks! edit: am considering 4.11 rear gears and tremec tko 5 speed 2.66 first.