For whatever it's worth, that 5 speed is most likely NOT an overdrive transmission. The one's I've seen had a 1:1 Ratio 5th gear. Someone told me that an overdrive was optional in the heavy duty trucks. No idea it that is true or what years overdrive would have been available.

Back years ago, a local guy claimed he installed an industrial / heavy truck 413 engine and 5 speed transmission in a pick-up truck. I have no idea how many parts he had to swap or how much fabrication he performed. His Dad owned a salvage yard, so he had acres of parts available!