Re: High Thrust Prop for 6hp (1968)
I think you are looking for the lowest pitch propeller which would be 8.25 X 5 pitch and would be found on OEM propeller number 0386587. They are hard to find. Try sea-way.com in Seattle WA.
The next lowest pitch is Michigan wheel # 012068 which would be 7.75 X 6.5. These are also hard to find.
The next up is 763588 which is 8 X 7. and fairly common.
As far as fit, propellers that fit 1966-1979 6HP motors also fit 1958-1963 10HP motors and 1964 - 1973 9.5HP motors.