Dan,
That cross brace was modified to fit a set of headers from George (long story, don't ask) because my RF kit did not come with crossover headers, it was not an option back in the day. However, even though the cross brace was modified they still didn't fit George's headers, so, in the end I was going to end up making a new cross brace. I think you will too, unless your headers will make it but I don't *think* they will because I thought I remember fitting those up.
IMHO those headers you have are one of the best sets I've ever seen for a RF - they are vrey tight to the block/valve covers and run low so as to not interfere with the back deck at all (Hershal had that problem with his headers due to one or two pipes being high). Still, that brace didn't work but I think you can make a brace that goes OVER the headers - sounds crazy, but those headers are very low and tight.
Ron