I'm assuming you mean the transmission cross member. You'll need a cross member for the 200-4R trans. They're different from the the TH350 type cross member. Having the frame extension is a good thing, especially with your car being an earlier G-body that did not have the built in frame extension on the left side.
As for x-members, you can try Iceman. He makes a quality product. The type he makes now is a tubular unit compared to the old G-force type member.
http://www.maliburacing.com/iceman/
Or you can take the one out of your parts car and modify it to accommodate duals.
I see that G-body-vet has got it covered.. and is absolutely correct. The TH400 unit can be used with the 200-4R. So the Jeg's x-member might be a good choice.