Re: forward thrust hub
The prop # you listed is for a "regular" lower unit(not bigfoot). That # corresponds to a 9-7/8 X 13 pitch black diamond prop. Is your motor a "Bigfoot"?
Since Merc and Michigan props generally use the same thrust washer, the Michigan thrust washer # is 16145-2 for that motor with the regular lower unit.
If it was me, I would slide on down to my nearest Mercury dealer and get the correct Mercury thrust washer and/or prop. If the thrust washer fits on the lower unit, but not on the prop, it sounds like you got the wrong prop; i.e., thrust washer too big for the prop sounds like you have a bigfoot and you're trying to put the regular(smaller hub) size prop on it.