No, a factory-installed overdrive transmission wasn't available for the 1979 Ford F-250 with a 351M engine. The common transmissions for that truck were either a 4-speed manual or a C6 3-speed automatic, neither of which had overdrive. Overdrive transmissions became more common in the early to mid-1980s.
You could *add* an aftermarket overdrive transmission, but it would be a significant modification requiring a new transmission, driveshaft, possibly modifications to the transmission crossmember, and potentially other adjustments.
