Does the rotor spin when you crank the engine? If not then you broke the left side timing belt.
Can you get spark to the plugs as a timing light will show you, by plugging into each plug wire and grounding to plug? If yes, then you can check the timing at about 24 degrees BTDC, for No. 1 (front right) cylinder. Best to put some white paper white out paint on the 24 degree mark first. If you cannot see the white mark then your timing is way off, perhaps the timing belts jumped a tooth.
The GL10 distributors have a short life expectancy. Better find a backup to always have on hand and to install here. If you have no spark and the rotor spins, then you probably have a bad cylinder. Buy used from John's Subaru in Laurelwood, Oregon, or get hosed on Ebay.
Wires that get hard, brittle and stop conducting electricity are the hot wire into the back of the alternator, the engine ground wire at the body end, and the hot wire from the hot battery terminal wire to the bottom of the fusible link box (at the terminal wire end).
The timing probably got off somehow, perhaps from the timing belts loosening up that allowed the timing belts to jump a tooth. Adjust timing belt tension in the front rubber pop out covers, with a 12mm socket, and don't lose it inside of the covers.