There never was a gray engine block color on Mustangs. What you are thinking of is oil pan. In 1982 Ford quit painting the engine blocks and only painted the oil pans while they were bolted to the engine. Of course there was overspray on the engine block and timing cover. During the 1993 model year black became the color of oil pans and valve covers on 5.0L Cobra engines and some 2.3L engines. All engines from 1982 have natural cast iron blocks and heads. Intake manifolds were also unpainted. 3.8L V6 engines had black oil pans and valve covers. I hope this helps out.