I bought a stripped barrel with Barrel extension installed and headspaced and the index pin and the gas hole are not exactly Top dead center.They are off by 2 degrees.I was told the gas hole must line up exactly for proper function.Is this true or will it be Okay with GI gas block?Should I return it? Any answers appreciated.

Two degrees off on the gas hole is no problem.  The hole in the front sight tower is larger than the hole in the barrel.

Two degrees off on the front sight would move the top of the sight by .087 inches or about 31 clicks of windage.  (I don't think the rear sight has that much range.)

The manual says the zero should be within 12 clicks.

One possibility is to use an Armalite front sight tower that clamps on the barrel rather than using taper pins.  Or, the barrel could be reserved for a flat top upper using a scope and shaved front sight.

I agree, go with the Armalite sight tower that clamps on.  I installed one on a crooked bushy.  lets you get a mechanical zero.

Thank you guys,I will get a clamp-on gas block.Regards