According to Advanced Auto the '83 Maxima Diesel pump has the same part number for a '72 240Z.  It's a remanufactured Atsugi if you look at the pictures.

 

http://shop.advanceautoparts.com/p/driveworks-water-pump-remanufactured-57-1016/20420100-P?vehicleIdFromReq=-1&isAllVehicle=false&vehicleIdSearch=18855&searchTerm=57-1016&showTitle=#

Would you have alot of confidence in a $19.99 rebuild?

As long as it's a cast impeller I think I'd trust it. They're so easy to replace also and with 30 percent off coupon code they're $14. The same pump made by Asin is $65 @amazon.com.