There is a possibility that a 707 was still available later for fire apparatus. Back in the 50's, as now fire insurance is rated by the fire equipment available. Insurance companies gave low ratings to Diesel powered equipment because it wouldn't start in cold weather in those days. They also had guidelines as far as displacement for different gpm pumpers. There was a category that required a 700 cu in engine which made the 707 Mack a popular engine for fire apparatus. The 5" bore 6" stroke Mack was a very durable work horse, but I don't think it had anything to do with GMC. It could have been that GMC still produced the 707 for fire trucks, but they really pushed the 71 series Diesels in their highway offerings because they owned Detroit.
