difference between pre-1984 and post-1984 Mariner (Yamaha) 9.9M OB shaft??

[scarface]

I have a 1980 Mariner 9.9M 2 stroke that was built by Yamaha on my Avon RIB. I need a new prop but I cannot find anything for a pre-1984 motor. S/N starts with 682. Going from memory, I'm pretty certain the S/N is 682CS 01809. I haven't taken existing prop off to verify just yet, but I think it is an 8 tooth spline shaft. Will check for sure this weekend at marina.

Any knowledge, links or info for a replacement prop would be very much appreciated!!