thinking about swapping the 12 bolt 3:08 pegleg for a 3:55 posi unit.
i still like to drive 70mph = 3000 rpm now. so i guess if i went to the 3:55's i would run somewhere around 3450rpm @ 70 and about 3000 rpm @ 60 mph. see myself taking maybe 2 - 150-200 miles trips a year and the rest is around town. would this long trip be hard on the 396? how about 3500 vs. 3000 rpm? it has been balanced and has a 280h comp cam. not sure what the CR is, but the motor is a '69 396/350 hp and it has a Richmond T10 manual 4 speed.
Your car will be just fine. Big blocks and 70 MPH were prevelant in the early 70's and worked just fine then. If you want the best of everything, leave the ratio alone (add the posi)and swap in a Doug Nash 5-speed. That's what I did with my Chevelle SS 427 convertible.