Eddie,
I took those pictures to compare the assembly-line GM tank with a reproduction. Having reviewed the details, I'm not so sure that your tank is repro..... could well be over-the-counter.
Here's the differences that I noted (the GM tank is dated '21 69' and it came off a January car, 01B if I recall correctly).
1. Original GM has a 1" wide collar at the filler inlet, the repro is 1/2".
GM:
Repro:
2. The rebates for the gas cap in the filler neck have different orientations, at approximately 11- and 5-o'clock on the GM tank, and at the 9- and 3-o'clock position on the repro.
GM:
Repro:
3. The locking ring for the sender has a number ('16 9') on the GM tank, and nothing on the repro; also, the spot welds either side of the 3 locking tabs are much smaller on the GM tank than on the repro.
GM:
Repro:
4. On each side of the GM tank, the joint seam has a transition from horizontal to almost vertical, approximately half way along the tank edge; the repro seam is flat along the entire length.
GM:
Repro:
5. The perimeter seam has a different appearance, the GM tank has what looks like fish scales, like a weld run, but the repro has like a crimped appearance with a regular series of perpendicular 'ribs'.
GM (probably should have cleaned the tank to better show this detail...):
Repro:
