I didn't need to remove that cross-member at all, there's just a little plastic clip to pull that holds the harness for the rear sensor which sits above the cross-member. I sawed off the tail end of the old cat just forward of the cross member and the old cat came out OK. Then after removing the rear clamp with a dremel tool, the stub was welded to the muffler. Things seemed pretty gloomy
until I heated the junction cherry red with MAPP gas and put a 14" pipe wrench
on the stub and voila'! (I was careful to avoid having that hot thing land on me!~)

Now I snapped one of the studs in the flex pipe and tried to heat and remove, but
there was little room to swing vise grips so I decided to reassemble with three
instead of four studs.

The next disaster was when trying to remove the plug for the front O2 sensor in my Bosal Cat Converter.
First: I got the Allen key and a ball peen hammer.....nope
Second: I got the BFH (32oz ball peen which usually convinces stuff)... nope
Third: I heated with MAPP gas and used the BFH......nope and now the allen key
and the socket head are starting to deform GRRRRRRRR
Fourth: I took it down to my mechanic Guru and he tried moving it with a
combination of of an air chisel and an Oxy/Acetylene torch...it
did budge a tiny bit, but still no joy
Fifth: we drilled out to 1/2 ' the largest drill bit we had and while
he was looking for the right tap drill for the 18MM thd, I took
it home an used a saber saw to put two cuts through at 180 deg. and
knocked the remains of that SOB out.
Grrrrr! I expected that the way my luck was going, that a giant meteorite
the size of a Volvo was about to strike any second.

The rest is boring, It all went back together uneventfully.
The Wagner clamp was crap, so I reused the original clamp with some new bolts
and the joint is noisy. So I wonder if there's a trick with that clamp, maybe using muffler bandage or muffler cement or something?
Tomorrow I'll see if it passes state inspection, and find out about the noisy
junction- Cat to muffler.