Need help with fuel sending unit

[GT350Mike]

The original sending unit has never worked since the car was delivered so they shipped a replacement (the unit on the right, part # SUP04-90-240-33). When I compared it to old unit, my first question "where's the disk that fastens to the end?" then it dawned on me that it's probably inside the tank. I also noticed the end of the old unit was ground down as if it was rubbing against the bottom of the tank, which I confirmed when I tried to install the new unit becaues it too was bottoming out on the tank. Apparently, the aluminum tube is either too long or mounting hole for the sending unit is too low.

As far as solutions, I might be able to bend the aluminum tube back so the tip will clear the bottom of the tank but I'm concerned about breaking the electrical components. The only other solution is to doublestack the cork gaskets, but I still think i'll have interference problems. Any ideas?

Almost forgot to ask.....can anyone tell me the purpose of the disk?