Vintage Steinway

[A440A]

Inre broken let-off screws:
<< I need to extract them , obviously, and I was
thinking of using a soldering iron lightly to loosen the remaining
screws and remove the rest for replacement.  Ideas?  Comments?  >>

     A micro torch will usually put a lot of heat into them in a hurry. If the
rest of the action is removed, you won't start a butt-fire (!).  Otherwise, a
soldering iron is the way to go. 
    It helps, when removing a screw like this to clamp small vise grips on the
protruding part, and then after heating it, wiggle it BACH AND FORTH, not just
turning it one way.   This back and forth movement grinds a little clearance
around the threads and often will let the screw begin moving freely.  You want
to put as much motion in as you can, but really don't want to break the
remaining screw off.  
Good luck, 
Ed Foote