You may or may not have to pound the firewall to make the O2 fit. And yes, sometimes the crossover pipe will not line up. You will need to bend it and loosen everything and get it close as possible and force it togther. TOG's are so expensive just stick with the SD setup.

And I mean really, are you gonna spend the same amount of money on a single header than for a whole setup? And TOG's look like something I could make...