I've been unsuccessfully trying to get my '66 Sport Fury with 383 started after a short hibernation of about 20 years. At first, it was cranking normally. After several cranking attempts, I started getting a spark and smoke from where the battery ground cable is bolted to the thermostat housing. The cable is bolted tightly(in fact, I haven't been able to budge it). Coincidentally, this started at the same time the oil light decided to start working when I turned the key on. I've never seen anything like that before. What would cause it? Also, I'd appreciate any ideas on removing the thermostat bolt.

Thanks,
Harold