I acquired an 11.5" heavy barrel that I am going lengthen to 16" by permanently attaching a fake silencer.

The person I bought the barrel from said that it did not have a "gas port" drilled in it yet.

All of the diagrams I have seen show the gas tube coming straight out of the front of the upper receiver, and into the front sight.

Is there supposed to be a small hole (drilled into the barrel) under the front sight base?

The only hole drilled into my barrel (except the bore) is a small hole where the barrel-centering pin should be. This hole does not go all the way through to the bore, I would guess it is about 1/8" deep. Is this some kind of defect, or can I just fabricate / buy a centering pin to install?

Any help would be greatly appreciated!

Yes.

Sure does.  

Without the hole under the front sight the gas tube won't have any gases flowing back to the bolt carrier and therefore it will not cycle.  

Yes

Thanks guys. Being a newbie is a bitch.