The drive shafts are the exact same,but there are many more changes to be made.It would be the easiest to find a 1969 40 horse with manual shift that has a bad head and swap out the power heads and the remote control unit.
You might just as well get a complete working 69 40 horse.It would be less trouble and you can sell or keep the other for parts.
The motor runs perfect in reverse and at 1/3 and less throttle in forward. I omhed the wires by the powerhead they were at 8 omh's. I filled the lower unit with 75w/90w synthetic. The motor runs so good i would hate to scrap it?????
According to my Seloc book they didn't make a manual shift 40 h for that year, I have a super sea horse 40 but not sure the year, It looks the same vintage