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Assuming you didn't pinch or break any of the wires that are behind the battery tray, it sounds like a bad ground. Make sure all the harness behind the battery is good by taking the battery back out and looking everything over. Make sure you didn't damage the coil connector when replacing the battery either. If all looks good, reinstall the battery and make sure the connections are tight. fire it up and see if it has straightened out. Post back with results.
Ok. Just post back when you check everything out... It shouldn't be anything to serious. My '91 GT used to give me a fit like that occasionally. Usually something simple. They really are pretty dependable cars and the 302 will flat take some abuse!