my usual get around driver/highway use 440/auto worked really well with a 323 and was ok out of the hole. if you are set on replacing the 391, get yourself a drop in 355 gear. i have used these in a regular street driven setting and they are very nice for daily use and the occasional light to light. i find them to be a nice happy medium between street and strip use. keeeep the 391s so that you have options. hell, at one time i had a set of 323,355,391,410 all ready to go whenever i decided to change anything else up. those were the days lol
