I was reading all about your Black Sheep Squadron resurrection and enjoying all of the great photos. I picked one up last weekend and have been putting it back together a few hours a night.
Mine, S/N BSS1195, was another put away and forgotten copy as well. Stored without play field glass, it was covered in grime and all of the rubber was dry-rotted to oblivion. I had the same exact chime Coil/plunger issue as you but was able to McGyver a solution.
Were you ever able to find out more about Astro? Did you find a parts source? Do you still have the machine?
Main thing I am looking for is backglass. Mine looks ok until illuminated from behind, then it ain't pretty!
I also have a set of production and pre-production art for the backglass that I picked up several years ago. Happy to share images if anyone would like to see them!