I went out to the garage , forgot to change my clothes, I was just going to spray a little more penetrate on the bolt holding the reinforcement plate.
Well I could not resist putting a ratchet to the bolt. I forgot to take the deck off and just reached in .  It took a while to get the right extractor socket on the bolt .  9/16  to big , 1/2 to small.  You must be able to hammer the socket on to really get them to work.
After 10 minutes, I put my big wrench to it. The one that I am always told not use.  Well one click at a time the bolt came out. It took about 20 minutes to get it out, not hard , just one little click because of the tight space.
I was them able to remove the rusted mount reinforcement plate . Once removed , I will be able to put a small piece of fiberglass over the hole to hold the nut in the cage.  The cage was not rusted .  The new reinforcement plate for the # 4 mount will secure the bushing to the body.
I will then be able to fabricate a retaining plate for the # 4 frame mount which had a rusted out hole.  The mount is good.  I will get the plate welded to the mount once I have the car on the road.
I was very fortunate to not have a rusted out deck hinge area. All the rust was in the wheel well, except for the retainer bolt.  It  was only a few inches away from the rusted bushing.....
Here are the photos
Ratchet in place  with a little hammer to hit socket on to bolt
View of position of extraction
  
The rusted plate # 4 
 
49 year old bolt with very little rust 
The old bushing and plate
# 4 mount after clean up
Close up of nut and cage - rivets still holding it in with very little rust
View from below of mount