I just cleaned out the fuel tank on my 79 Monza wagon and when I started putting it back together it seems I'm missing part of the sending unit retaining mechanism. I can't find any pics to help me identify all the parts I should have. I have the pump/sending unit that sits down into the tank, but isn't there supposed to be a retaining cam or ring that goes over the top of sending unit base and locks into the ring that's attached to the tank? Does anyone know where I can get manuals that would show this type of stuff? I have a Chilton's repair and tune-up guide but I really need something a bit more in depth? Thanks for the help.