I experienced the same thing. I ended up taking the rear brake off and slipping the exhaust off the bike whole.
That way I could try to separate the pieces later. I tried soaking the joints in ACF-50 (penetrating oil) and was forced to use heat to separate them.
Luckily I work at a shop that has a gas torch. Once heat was applied it came off with one tap from a sledge.
Maybe you could take the exhaust off (same as above) and ask some folks at a muffler shop to heat it up for you.
You'll be surprised how many people will rally behind you, if you explain that you're rebuilding this bike...
Upon refitting use Nickel Anti-Seize Compound on the joints.
Next time you won't have to fight. The company from the link above has a location nearby, but this is what I saw on E-Bay with a quick search.
What other work are you trying to do?
Thanks for the help! The list of to-do's on the bike goes like this:
1. new shocks - previous were terrible
2. now a new exhaust, probably a 2 into 1
3. full tune up and cleaning of outside and inside of engine
4. new paint, going red.
I will post some more pics soon.