I then tackled the elastic issue. I went to my local Michaels Craft Store and bought a 48" package of 1/2" elastic from the sewing aisle. It only comes in white, so I had to also buy a small bottle of black fabric paint. Cost: about $7 total. I then soaked the whole strip of elastic in the fabric paint and let it dry on the rack outside in the sun.
Here is the shoulder belt in it's original state. As you can see the 7" long section of 1/2" elastic stretched out to 20" of 1/4" elastic over 35 years:
I gently trimmed the factory stitching from the elastic and removed it after marking the area with some chalk. (There is a left and right belt and the elastics go on opposite sides). I then cut a section slightly longer than the original distance between the two mounting points, folded the ends and hand sewed them onto the belts. Here is the finished product:
The whole set is now all finished and ready to go. Though I could use a couple nicer satin finish covers in case anyone has an extra few just lieing around the garage somewhere taking up space.