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The only suggestion I have is get one from the junkyard to rob parts out of and compare component values. Ford contracts out people to work on their radios, and they are not very forth-coming with info and schematics(been there tried that).
With aftermarket systems being so cheap, and labor so high, it's not worth sending them out for repair, unless you want to keep it all original(which I can appreciate).
You can try this link to see if there are any yards in your area that may have one of the units you are looking for. www.car-part.com
Do you have a picture of the Capacitor at all? more than likely all you need to do is get close to the original size, mainly the physical dimensions of the cap as do where it will fit, also check with some stereo shops, they may have some old stereos that they remove when doing installs.