good question i've thought about it before but just figured you're limited by what the manufacturers sell .... unless you've got the $$ to get a custom set made up
not hijacking the thread but maybe helping by chasing a little more info ..........

what benefits do you gain from 4-1 or 4-2-1 extractors ??

in 4-2-1 sets how do primary and secondary tubes lengths and dia's vary the performance ??

and ... in using the orig 'GX' exhaust manifold what secondary tube diameter and lengths would be beneficial ??? and any idea on what the original ones were ???

any input would be fantastic