A 45* bend on the end of the exhaust tube or a narrower type might help some. I had the same issue on my '91, no header, but ran 2" straight pipe from a turbo muffler all the way back. I put a 45* bend in section and welded it on the end and it seemed to help a quite a bit w/low end power.
I am not sure how well a narrowing type would would work, it is what a custom muffler shop recommended doing, the owner said it is what they run on race cars to help out with the lower rpm range.