James, check out this link to Bob Westermans 3A fuel pump page. Very detailed.
http://www.cj-3a.com/Fuel%20Pumps.htmWalcks has a rebuild kit for $70 and the whole pump for $140.
I rebuilt a AC 4032 wich is also a vac/fuel pump using their kit and the parts are very good quality. The pump I have has the glass filter bowl on top which is no longer available and why I choose to rebuild it instead of replacing the whole pump.
If you go this route, you will need to remove the vaves which are pressed into the pump casting and only acssesable from one side. I pulled these by removing the small diaphrams and springs with needle nose pliers and then tapping the valve body with a 7/16" F.T. bottoming tap and driving a bolt in to lift the valve out. The oil seals on the diaphram shaft pulled out with a small hook tool. Remember to keep track of the direction the vavles are facing, ( I took pictures) before you pull them.
Matt