Fluid Private messaged asking me to review the post for my opinion, so here goes.
With a 3.42 you have the best all around. You have an effective starting line ratio of 10 to 1, which for reference, is lower then a 69 Z28 or 70 LS6 Chevelle (9 to 1) with a 4.10 (Muncie had 2.20 1st ratio), so you will have great low end grunt still, but not so much that you over power the tires all the time. Any lower gear may make the car to torquey to launch. It also would force a shift 20 feet from the traffic light, you probably would end up leaving in second often when you feel lazy.
On the other side of the coin, I like the 3.42s on the highway because at 60MPH you will tach 1670, and at 70MPH you will tach 1950. I suspect for your motor to be 400+hp, the cam duration is around 225 to
[email protected], which means it would actually still lope at anything lower then 2000RPM or so, and loping and chucking at cruise speed is miserable, you could end up finding yourself in 4th gear a lot. I also suspect like most of us, you probably cruise at 77MPH more often then 70, so you will be a couple hundred north of 2000 at cruise. Based on the cam specs, (if the cam is over
[email protected]), I may change my mind and recommend a 3.55, and unless the cam was over 240@50, anything lower then a 3.55.