No. The factory rail has an integral regulator.

Is it at the end? If so, that will do.

Yes, it is.

if it is stock, then the regulator is mounted to the front of the fuel rail, so no you will not be pressurizing the fuel rail.

So I'm gonna need to plug the return line opening in VST tank?

Can envy one explain please what will all that do? I mean putting the return line from VST to the gas tank.
I'm looking at that picture and can't figure out in what way will it improve it.

Rather than sending the unused fuel in a continuous circulation loop around an 8.2L heater you'll send it back to the tank. It keeps cooler fuel going into the vst rather than recirculating some superheated stuff.

yes, youll need a 5/8-18 inverse flare plug for the vst tank.

Ok. Now I understand. Thank you

What I was also thinking was replacing the spring in the VST for the weaker one. If it presses with less strength the vapor pressure won't have to be as big as with the original spring to open the vent valve. It will allow vapors to escape more easily.
What do you guys think?

I don't think that will help. A vacuum hose from the intake connects to theside of the top and pulls that diaphram open against the spring. It isn't pressure inside that opens the diaphram. You need to make sure there is vacuum on that hose and that the vacuum pulls the diaphram open. If it is leaking or losing vacuum, it probably still won't open it even with a weaker spring. In my testing those, I don't think it takes much vacuum to pull it open. I have one at my lake house that I could test this weekend if I remember to. Did you get a chance to test any of the other suggestions out?

Ok I'm little confused. There are 2 vent hoses. I'm guessing you are talking about the one that is not on top of the VST cover but one on the side. Right?
How can vacuum open that diaphram if it's being pushed by the spring from below. If suction is applied it will only close (suck in) that vent even stronger.
That makes me think that the spring should be on top of diaphram in my VST and when I start the engine it will be sucked in and close the vent. Once the vapor pressure is high enough (during engine running) it will push the membrane down opening a vent.
Please correct me if I'm wrong.
When I took VST apart the diaphram and a canal leading to that clear hose on top was completely clogged.
I'm trying to figure out one thing at a time. I boat every Sunday so it's the time of testing everything I implicated over the week.

Here is what I did. First, I was sick of paying $86 each year to replace the rubber diaphragm in the VST, Second i was sick of vapor lock. I fixed both in a hour. I ran the "vent" line with a non working diaphragm back to the tank, and plugged the port on #8 intake runner. Super EZ. A couple brass fittings, and zip ties to tie the line off so it doesn't rub on anything. I have it posted on another thread somewhere. One nice thing tho, my boat was already plumbed for twins. So I had a extra hole and fitting in my tank.