Glad to hear you worked it out.
Not sure what you mean by "back off on the muffler to get the headers in"??
I can think of two things to give you more room---one would be to take off the support brace on either side (re: if you haven't done that already) and the other would be to put the flange side in first and have it butt up against the cat end, then give it a little umph to get the manifold end in. (re: is this was what you mean??)
Anyway, looks like you're almost there!