what rear would you go with

Bill, considering the torque of a 440 big block I don't see why 3:23's wont's work real good with your 245/60 tires. They'll lower the hwy. rpm cruising rpm a lot over the 3:91's you have now and still take off decent. One thing you might try to get an idea how taller gears will feel is to slow way down to 10 mph, click it into 2nd gear then nearly floor the throttle but not so much that it kicks down to 1st gear and see how it feels. I have a mild 408 in my Cuda with 3:55 gears and when I slow down to 10 mph and floor it it still roasts the 275/60/15 drag radials cause it's torquey like a big block. Getting ready to put some 3:23's in it for more pleasant hwy cruising.