I've also heard of what Mike said about how to locate it. Awhile back, I worked in a shop that did custom exhaust, and we would recommend crossovers, and used the same method Mike described. While I worked there, I modified my wife's Mustang exhaust where the crossover was, and added a bolt-in flange to each pipe behind the crossover so I could remove the trans by unbolting the collectors, then unbolting the flanges that I added, to remove the "H" pipe. This would eliminate the problems that DZ mentioned. I'm sure a good exhaust shop would do it if you requested, for a nominal fee, I'm sure.