For a mild street car, a cone posi(ooops, sure grip!) should be fine. I would prefer the clutch style. Ive heard good, and bad, about the gear style true track. I believe Dr Diff isnt selling them anymore. If thats true, thats more than enough to keep me away.
Since i wanted as much strength as i could get , short of a spool, I'm using a locker (Detroit, or also Dapco, same company). I dont mind the snap crackle and pop, but for a mild 383, you dont need one. Lockers are for 75% strip/25% street cars.
Ive got a nine inch in another car, but i havent decided yet on a spool or drop-in locker. Im leaning toward the locker for the open carrier.
Above advice to call Dr Diff is excellent! Step one!