3.0 6-cylinder engine. What size fuel lines do you run from the fuel pressure regulator to each carb? I am running PMO carbs with PMO fuel pressure regulator. 9mm or smaller?

The PMO's should have came with instructions, RTFM.

I used 5/16" fuel line and it fit the stock nipples on the Weber carb's perfectly.
Use correct size FI hose clamps, never use worm gear clamps.

Be absolutely sure the fuel line meets current SAE spec. This fuel line is ethanol safe, but even with the correct line it's best if you can use pure gas.
http://www.gates.com/oreilly/tech_tips/Ins...uelLineHose.pdf

With the PMO regulator you can use an FI pump, but be sure to use FI fuel line between the pump and regulator if you do.

I use FI line anyway,but I have to say I did order the same with the outside nylon braiding always found that to be good.
IMO when the hose looses flexibility its on the way out.
Cohline is one of the bigger suppliers of hose but their product has shown to be inferior to modern fuel ,so I guess checking my hose regular is like checking water in an watercooled car ,it is a worry.
The fuel we get here is my country would most likely cause the same issues.

Thanks Mark. I actually purchased the carbs used so I dont have any documentation. I guess I could call/email PMO

I always give customers their documents, but I know for sure it said you can use an FI pump with their regulator, in fact it's no longer an high pressure pump with it. It does this because the PMO regulator bypasses just like an FI system, so you have to run a return line.
It has 4 nipples, one in, one bypass back to the tank and two regulated outlets, one to each carb.