How does my contraption look??

On the early cars with the stock sendin unit, I just drill a hole through the sender base and braze on a return nipple. A lot of the later cars have the vapor return you can use as a solid fuel return. But yes, if your cell has no return provision, through the top is fine. A lot of cells are much like a factory tank in that you can drill and weld in a return nipple right in their sender base as well. Done it many times.

Also, one VERY important point that I left out. Notice the BG diagram. In order for the fuel to go back to the tank through the return line, it must flow into the carb, then CHANGE direction, go back through the SAME way it came in and out the return line. That's a lot of turbulance. Routing the return line in the fashion I outlined allows the fuel to flow the SAME direction the entire route of the fuel system.