Re: 63 to 70 lower unit switch?
You could make the newer lower unit work on the older motor by modifying the later model's shift shaft, and plugging the vents at the upper rear of the gearcase. You'll also have to modify the older motor's reverse lockout cams and spacer "spool" so the lockout mechanism will work.
The older motor's lower unit will bolt up to the later motor, but it won't have provision for an exhaust tube so you'd have to butcher the later motor's exhaust tube and that's not kosher! Not sure if the shift shaft and reverse lockout can be modified to work with the later motor's lockout.
HTH...........ed
