Working on a 1957, Wizard Super 10, Model WH-7A. I need a Needle & Seat for the carburetor, AJ45B. Trying to figure out the part number for the Needle and Seat. The Mercury KH7, Mark 15, Mark 20 and Mark 25 all use part # 1399-1138. Though the Merc manuals do not state the carb model numbers. Please help.

I think this might be what you are looking for:

https://tillotson.ie/wp-content/uploads/2015/07/AJ-Series-Parts-List.pdf

Your carb is in the first column after the part name on page 11. Apparently the carburetor is rare. I'd keep searching "Tillotson AJ45B" on eBay periodically if you cant find the part by number.
-Bryan

THANKS Bryan! Great diagram.