Looking for 8.25 or 8.75 rear end

Im newer to this but still know a lot about cars. I am looking for a 8.25 or 8.75 rear end for my 1975 dodge dart sport. im pretty sure it has a 7.25 in it know becuase it was converted from a /6 to 318. i've read for better performance to go with 8.25 or 8.75 rear end. It has a tourqe flite a904 trans if that helps at all?
thanks dom