Can you get at the hinge pins of the 350? Did read somewhere that on some SOHCs it was possible to remove the two hinge pins and then turn the whole seat through maybe nearly 90deg to release. But you would need to remove the tank also I presume to protect. But may also improve access to BJs method to get at the nuts holding the pin to the pan. I think there is an offset pin in the lock that breaks.
Amazing when I re-read this. Remove the tank!! err how??