Ive heard that the commercial extractors available for the 2.4 arent all that good...
you might pick up some top end power, but realy who drives around at 5000rpm in a 16 year old car anyway....
and you will probably lose bottom end torque, which is the main thing these engines have a good reputation for, power down low is good!!!!
custom is the ultimate way to go.... long narrow 'runners', 4-2-1, with the lengths staggered to the order of the pistons firing... like 1423 or whatever they are