What 6 cylinder inline Mercurys from the 1950’s used a 7/8” diameter driveshaft? I’m trying to mate an early Speedmaster lower unit with a 7/8” driveshaft to an appropriate 6 cylinder inline Merc.  The Mark 75 shaft is too small as is the Merc 700 direct reverse model. I believe the Merc 700 full gearshift model has a 7/8” driveshaft but need this confirmed.

Thanks,

Frank McCarthy