Factory fuel injection 5.2 magnum using external electric fuel pump ?

i think the supply is 3/8 and return is 5/16 stock fuel line on truck.

That is correct. I removed the 5/16" return tube and installed a 3/8" return tube in the sending unit using silver solder to seal it. I had to go to a welding supply store to source the real silver solder.

Sending unit mod 3.jpg