With a 350/350? In a 2500 pound car? No way is any type of locking/posi diff necessary or even desired unless the car is driven in snow or torrential rain. Anything but an open final drive will exacerbate bump steer and potentially lead to serious consequences if an axle were to break and this is an 8" he is talking about. While the 8" R&P itself is very strong, the axle shafts are less than great unless they are aftermarket, i.e. Currie