If it's like my RENIX XJ's, that flange is ctually part of the catalytic converter. I see three options:
1) Check out your local salvage outfit for an old cat, and cut the flange off. Have an exhaust shop weld a pipe stub to it for you, and use that.
2) Cut off the mating flange, and go pipe-to-pipe (which I'd sooner not do, but I've got a 5-speed and that flange makes changing the clutch easier...)
3) Take dimensions in to a machine shop and see if they'll make something for you out of 1/4" or 3/8" mild steel. Take it to an exhaust shop and have a pipe stub welded on.
I've toyed with making a batch of them next time I get into the machine shop, for just this sort of occasion...
BTW - How'd selling that damper on Ebay go? I hate being broke...
5-90