Hi Terry,
Rebuilding is the cheapest option. The short coil from the later SU pumps will go on to the square bodies. You can buy cheaply and canibilise a round body AUF300 series pump from auction sites. They are plentiful.
I would just rebuild a complete AUF300 type in the short term, and look for a suitable square body on auction sites for longer term.
Lots of info in this thread and others: [xk] Fuel Pumps - #18 by jav250, SU Square Body Fuel Pump - #8 by clivejer.
Regards,
Clive.