Hey, Lou...
As you have a new x-over pipe, it would be fairly simple to use a Dremel cut-off disc (or similar) to make a couple longitudinal cuts on the old pipe where it joins the header. Perhaps even saw through the middle of the x-over to allow a bit of twist n' turn to remove the old bugger.
Try some PB Blaster -or a 50-50 mix of lacquer thinner and ATF- as a rust buster after making the shallow cuts.
Obviously, you'll need to remove the headers to install the new, shiny x-over. Does the new bit have the
"bolted tubes" as the OEMs?
Luck with the header clamp nuts

Monte