The factory tests that were done on the 22 Cruiser with the Honda 75 used a 13 3/4" x 15" 3-blade aluminum prop. That's what I use on my setup, which is the same as yours (2001 Cruiser with Honda 75). By the way, your speed is probably right on, when my tach was misreading, my speed was accurate, the tach was just saying I was doing that speed at a lower RPM, that's why I'm pretty certain the set position for the tach is just incorrect. My tach too read around 3,000 to 3,500 RPM at WOT when it was set to the wrong number on the back. I don't remember the correct number for mine (it's not here to look at, but I believe mine was off by 2 numbers, was at a 4 and should have been a 2 or was at 3 and should have been a 1 or something like that), but a dealer should be able to tell you which number that arrow should be pointing at. I think that will solve your RPM readings then.
Jack