Most fires in GM's in car from 60s to early 80's started in the cowl area. The wiper motor was the culprit on a high percentage of these. This area in the middle of the cowl behind the carb and distributor was where most started. It was also where GM routed wires thru the firewall on a number of models. Driving down the road the fire would start in the wiring and then forward movement of the vehicle would force the fire inside burning along the wiring harness, melting the plastic (or wire reinforced mesh) HVAC ducting and then up the defroster on to the windshield...