Ok. So, you can easily lengthen the pick-up, but not the level sender.
If you look at the pick-up assembly, you have to metal fuel lines. The big one on which the pump is attached sends the fuel, the small one is for the return.
There is a rubber hose that attaches the fuel pump to the metal hose above ( you will need a longer rubber hose of the same diameter and two hose clamps, how much longer? It depends on how much deeper you want the pick-up to go). You will have, first to cut the small (return) metal hose with a metal saw, approximately at the same level as in the other side. You now need to connect with a rubber hose the two ends you have just created on the return side.
Make sure that the pump is still grounded, remember that you have cut the metal hose on the return side.
If you have any more question, feel free to ask.