Help locating Blazer bed hole(s) for Fuel tank.

[Accelo]

I am getting ready to punch the holes for a Blazer fill in the bed. Can anybody help out with the hole locations and diameters for the holes in the bottom of the bed? I can best guess it but don't want to do that unless I have to.
The assembly manual gives only the fill assembly information. I am including a picture from a Blazer fill taken from the inside of the bed. It's a California 1972 truck.
I unsure what the exact reason for the round tube in back of the fill. I will not be installing that as it is likely a CA only emissions addition. I am only interested in what is under the rectangular cover piece.
Thanks

[Richard]

Yes the small tube brings vapors to the top so they can be recovered. But it also allows faster filling. Provides a direct path to the inlet for the air displaced by fuel. If it is not there the air has to makes its way back up through the fuel you are putting in. I would not eliminate it. Emissions or not.

[kwmech]

Originally Posted by Richard

If it is not there the air has to makes its way back up through the fuel you are putting in. I would not eliminate it. Emissions or not.

Exactly, the tube helps 'burp' the tank while filling so you do not get back splash out of the nozzle

[Accelo]

I understood the reason for the small line that goes into the top of the fill. The other round tube at the 8" mark is what I wasn't clear about the use. Does that clear it up some? It has fuel lines connected to it from the bottom.
I do appreciate the feed back.

[Richard]

Okay, understand now apologize for the confusion. See it now, that piece does not look factory. You said "lines connected at bottom" I take that as multiple. Where do they go? Factory tank or aftermarket? How does it attach at the top? Sorry for all the questions never seen that before. Factory tank would not need anything different even in the republic of CA.

[Accelo]

Everything appears stock and not modified. Even has factory appearing clamps. It does list CA emissions on the SPID. I never traced them out but assumed they went to the fuel tank. I should have gotten a picture from the underside.

[Thealien]

That is factory and part of the gas tank vent and emission system. There are two vents from the gas tank that both go to that tube. Then one line goes all the way to the front to the charcoal cannister which when working properly will burn off gas vapors/fumes while you drive.

Over time many of the vent lines in that system get clogged and can cause problems. Sometimes you can blow or clean out the metal tubes and replace the rubber lines and get it working properly. There are some discussions on taking the charcoal cannisters apart and putting new charcoal inside.

There are 3 ports at the charcoal cannister. One goes to the line from the tank and that tube. 1 line goes to manifold vacuum, and the third line goes to ported vacuum so there is only vacuum to the charcoal cannister off idle I believe?