The simplest way to work with a stripped nose bracket is to slip a smaller size vice grip between the rails onto the tail and properly attach (not too tight). Never fails and allows 2 free hands to hold saddle and work spanner tool. Saddle should be off bike obviously.
I just got my 70s Competition back from the shoe repair shop with a new strip of leather over the nose with new rivets. $25 and it's a brand new FUNCTIONAL saddle. The older rivets were about to pop out. Not sure how many thousands of miles are on this one. I've owned it for 20+ years.
Kevin McCaul
Silver Spring MD USA