No the 18-2686 is for the 25/30/35hp Motors.
Sierra does NOT make a kit for your motor.
You can buy the 18-2684, but the prop shaft seal will not be correct. You will then need to also source out a 302495 prop shaft oil seal to replace the one that comes in the kit. Sierra does not make this seal , so that is why they don’t make a kit for any of the ’51 to ’57 10 to 18hp OMC motors.
I make up my own kits if you are interested as well. PM me for details.