Check the link in post #4

http://www.peachparts.com/shopforum/body-repair-restoration/311980-how-fix.html

I know there was also another recent(ish) thread where someone found a good panel in a JY and just cut the necessary metal out rather than fabricate a panel.

There was also just a link about replacement sheet metal panels for the W123. Depending on scope of damage, that may be an option: buy a whole 'new' panel, but only cut out the necessary pieces to weld in place. That way you wouldn't be fabricating, nor would you have to hunt in a NE yard for a rust-free panel.