Having seen a post from andharri2 on Dec. 2010 regarding how to remove and reassemble the swing-frame pivot, I undertook this project and have provided some pictures that may help others do this job.
I'll start by showing the pivot parts, removed, as an assembly, show a tool I made to remove this assembly, and show how it all goes together.
This is a picture of the pivot part assembly. It consists of two nylon bushings tightly slipped over both ends of a hollow metal tube. A metal rod, threaded on both ends, goes thru this tube, and this rod is secured on both ends, via right-hand threads, with those round "nuts" with the 4 holes in each. These "nuts" have a large boss on their inner side, which is used to align the lower swing frame with the upper frame.
The next pics are of the individual pieces.
Here is a pic of the bushing assembly installed in the lower swing-frame.
To remove these "nuts" I fabricated a tool using a piece of lumber and (4) roofing nails, "11" Ga., and 1-1/4" long. I drilled (4) holes in the lumber in the same pattern and with the same spacing as the (4) holes in the round nuts. I ground off the tips of these nails and hammered them into the holes. I used tape on their head side to help keep them from working their way out of the lumber. This taped side is shown below (tape removed for clarity).
Here is the "business" end of the tool. The (4) nails shanks will align with the (4) holes in the round "nuts".
This pic shows a "nut" being gripped by the (4) nails.
Now the tool is placed against the nuts with the nail shanks penetrating the holes. Sorry, this pic is a bit blurry.
A pic of the tool from it's outer side. Notice the tape helps hold the nails in place. I drilled the holes a size larger than the nails for fear of splitting the lumber.. The length of this lumber gives it some leverage.
An alternative to making this tool may be to insert (2) of these nails into the nuts and using some pliers to grip and turn them. Four nails will give a better grip.
Use the tool to unscrew the nuts, counterclockwise. Removing one nut will suffice, since the other will still be attached to the threaded rod. Pull out the rod and it's still attached nut, and the swing-frame will pull away from the upper frame. Pull the nylon bushings out of the frame. You may need to gently tap on the metal tube that is inside the bushings in order to push one of the bushings out. They may be tight on the tube, so use patience and care not to damage them.
Next is the upper frame, empty of all pivot hardware.
Once all parts are removed, gently clean everything with a non-solvent based cleaner. Remember, those nylon bushing are 50 years old and need all the care they can get. Lubricate everything (I used silicone grease) and reinsert the bushings.
The next 2 pics show the upper frame with a bushing in place.
Insert the metal tube into the bushings.
Slide the swing-frame into position over the pivot assembly.
Insert the threaded rod thru one side (have one round nut already installed on one side of the rod).
Screw on the remaining round nut and tighten. I do not have a torque recommendation, but have it just so the swing-frame does not feel loose. Too tight and damage may occur to the bushings.