OK, I found the index marks right where you said.  They were hard to see because the barrel/receiver had been re-blued.  The marks are perfectly lined up.  So I guess the rear sight being a little to one side was within tolerance.

But I think whoever cut the dovetail for the front sight didn't get it aligned with the rear sight so I'll get either a 1903 or a 1903A3 front sight.

Thanks for the helpful replies!