Nissan ships with the 8" prop and that is what you get even if you order the 7" , you or the dealer has to install it .

Check for all the dealers within 100 mile radius and call them all, or as far as you are willing to drive!

If they combine the order (2 or more motors) there is no shipping costs according to my dealer.

As I said before , " if they are not aware of the options , they are probably not much of a dealer/service center" and don't talk to sales-persons , talk to the shop foreman. They are in sales because all they can do is BS in most cases.
The guy I got mine from answers the phone , sells the motors and fixes the motors .