From a friction loss standpoint, having a 3/8 outlet from the tank will not kill the effect of having a 1/2 inch line the rest of the way. In other words, changing the tank to pump line out from 3/8 to 1/2 will help if you are losing pressure at the carb under full load conditions. Then if you still have problems, you might want to go through the trouble of changing out the sending unit to 1/2. Unless you are running an all out, high RPM race motor, or nitrous, I think a 3/8 sending unit and 3/8 line to the pump will ensure low friction losses at high RPM. What the factory put in an LS-6 is good enough for me and my 502.
John Walker