I have a 67 b-body with a 440 that I am running a holley Red pump only. I believe it is regulated at about 5 psi. I have read about return lines and i think I am going to put one in, am I right in thinking a fuel filter with a vapor outlet plumbed back to the tank will do the trick? A few years back I installed a new 3/8 pickup line and left the 5/16 one on the sender unit. Can I just plumb into the old pickup line? Should I cut it just inside the tank? What are some of the bennies of a good return system? thanks for any help you can provide.

You can definitely run the return line as you're suggesting. Ideally, you want to run the fuel pump full blast all the time, use a return style regulator (or log), and run the return line back to the tank from the regulator.

Benefits are longer FP life, full pump volume available at any given time, noticeably cooler fuel, longer needle and seat life for the carb, sometimes less FP noise, and probably others I've forgot about.

The length of extra line is kind of a pain and might seem a little redundant, but it WORKS and it's well worth doing.

The biggest single advantage for vapor return from my seat is NO VAPORLOCK. First car I ever saw with a factory return was my '70 sixpack RR--my '69 383 didn't have it.

I wasn't sure how well it worked, until I'd put an "electronic" pump on in the early '70's. I didn't know these pumps didn't shut off, so I defeated the vapor return so "the pump would shut off." Not only did the pump NOT shut off, but if I didn't run the thing, the car would almost guaranteed vapor lock with only the engine mounted pump!!

Should the return line be from the pump side of the regulator or from the carb/regulated side? What size is best for a return line with 3/8 fuel line? Thanks for any info.

typically, the return line is 1/4" if I'm not mistaken.

I was planning on upgrading my 5/16" fuel line to 3/8" and using the 5/16" line as the return. The restriction is in the vapor separator so the size of the line isnt that critical.

The factory method was a restriction off the regulated side of the pump. Similar to certain 440 and 426 cars, and mid-late 80's 318s that used a vapor separator style fuel filter. That's the least expensive way of doing it and it works well.

The more expensive way to do it is to use a real, live return regulator such as this one and run the return line from that point.
If you want 100% of the pump volume to be available at all times, this is the only way to fly. With this regulator the return line would be the same size as the regulated line.

If you don't mind a tiny percentage of volume being lost due to the return and need to do it on the cheap, the vapor separator type filter works fine.

Actually, even a T fitting on the regulated side (or on the output side if there is no regulator in the system) with a restrictor in the return line works pretty darn well and is very low buck.
I used that setup many years ago with a carter 4594 electric pump...3/8" regulated, 1/4" return, with an .080" restrictor in the return line, and no regulator at all.
Nowadays I prefer the fancier return regulator, and feel it's a better way to do it....but there are other ways to get the job done.

Does anyone have a part number on a filter with a 3/8 inlet outlet line and a 1/4 or 5/16 vapor return? thanks

It is pretty obvious when you see it.
It looks like the standard mopar metal filter till you turn the package on its side and you see a second line come off one side.
Bought a few by accident and had to return them to get the right one.
All the parts stores carry them.