Ideas on running a fuel return line

here's the layout, 72 Duster with a mild 318 replacing the slant 6 (had charcoal canister which is long gone) new tank and sending unit with a 3/8 out and 5/16 in, eddy 1406 carb and a stock style replacement fuel pump. Daily driver in the making.

I'm currently bending up 3/8 line and plumbing in a FRAM spin on filter to replace the stock 5/16 feed line and being I want to run a return now I'm trying to figure out how. I can't remember where I read it but I read that plumbing a return line will help fix vapor lock problems which would be great because I live in Texas and sometimes it gets kinda hot(!). Had serious vapor lock problems in the past in my 68 Fury (no return system). I'm thinking the smaller nipple on the sending unit was for the vent or something to do with the charcoal canister. Do I need to need to add another nipple to the sending unit or can I use this as a return? Adding another nipple wouldn't be a problem if necessary. Where/what should I tap for a return? It's a single feed Eddy carb. Figure I'd throw this up while I'm out here bending and flaring...