Will this DC 4-1 header fit a 93 GS-R? If so, which application? 99-00 Civic Si? I am not worried about the cat bolting directly up to it. Taking care of that will be no problem.
I do not however want to notch the crossmember, or anything else along those line.
And I did try searching, but came up short…
It is my understanding that no 4-1 header will fit on our cars without modifying the crossmember. I believe you can purchase a new crossmember that is smaller and stronger and will allow a 4-1 header to fit. My suggestion would be to find a jdm 4-2-1 type r header. They are hard to come by but if you find one consider yourself lucky. Check out my review: type-r 4-2-1
I already read your review, and that header is on the top of my list. I just think I will have lots of trouble finding one… And if I can’t find one I would like to go with the DC 4-1. I suppose time is on my side, in that I have all winter to find one.
So, if I am understanding your post correctly, the DC 4-1 will fit with an aftermarkget crossmemeber that is smaller and stronger? Who makes them? How much do they cost? Where can I get them?
I remember talk of the aftermarket crossmember before. Try searching, if that doesn’t get anything then post up a question somewhere. 
i have it on my 92 gsr, it fits length wise, but u see how the flange for the cat is twisted and our cat is straight. after lossening the crossmember and notching it so the pipes wont hit(mines ugly, we cut it with a blow torch, lol). but yea, we had to re weld the cat flange to bolt up to the 4-1 header. it wasnt too bad, especially if your friend works at midas =)