Okay, I've seen it online in various sites and what not, but when I wasted 4 hours trying to get a 2000 ITR exhaust manifold on my 00 LS, I said F*ck you to all the sites and whoever else who thinks it bolts up.

Your best bet is to just get a GSR exhaust manifold gasket, and see if the holes line up with your friend's LS header, instead of wasting your time and labor.

If they line up, then tell me about it, and I'll admit I was wrong.