Not to rain on anybody's parade but when I looked at fitting a V6 box to my 2B the ratios just didn't give a big enough improvement to make it worth the effort. The first 3 gears are 8% higher and 4 and 5 are the same. Using one of the speed calc programs out there I would gain 2.5mph in first, 4.7mph in second and 6.8 in third, this is at 6k rpm with a 3.9 diff.
Ratios are 3.65, 1.97, 1.37, 1.0 and 0.82 for 2.0l.
Ratios are 3.36, 1.81, 1.26, 1.0 and 0.82 for V6.
Going for close ratio box would be the way to go but at around a grand it's just too much money for me.