Replacing the gas tank, Whats the deal with the filler neck?

[LuckyScott]

Took out a large aftermarket fuel tank. A friend gave me his old stock gas tank but he had removed the filler neck to use on his new tank.
Is there no company that makes a replacement tank with the correct filler neck?

I see on the box that the tank is supposed to fit blazer and suburban, etc.

I know I can take my old tank to a shop and have them weld on a filler neck, but between the floor and the frame rail it looks really tight and the welder will need to get the angle right.

Any tricks to helping the welder get the filler aligned and can I just buy a correct tank ready to go?