The first four gears in the Tremec 600 are almost identical to the wide-ratio Toploader. First gear is a little short with the 3.54 but still well out of the stump-puller category. I think using either a 3.31 or 3.54 differential would be acceptable.
Just remember that the .68 fifth gear is strictly a cruising gear - accelleration is only going to be noticed by a current Hyundai owner.
Unless your car is supercharged...
