A proper translation depends on the context. A 厂长 is the head of a manufacturing operation. In western countries, this 厂长 position is equivalent to the president or CEO of a company. The 公司 above it is a parent company. Use Factory Head as in the Chinese way, if you like. A term for a generic head position is director, as you mentioned. However, a general manager is usually a position under the CEO, who takes care of everyday operations in a company in the West.
