Problems with front sight post installation

[HoneyBadger]

I started with two functional uppers. One of them did not have an "F" marked front sight, so it wasn't usable with any of the rear iron sights I have. I decided to fix this by taking it off, and then putting on the "F" marked FSB from the other upper. All went well until I tried to actually put the new FSB on. The holes for "pinning" the FSB didn't match up. See pics:

Upper that had the non-"F"-marked FSB:


Upper that had the "F" marked FSB:



Is this a common thing or do I have an anomalous barrel/FSB combination? The "F" marked upper was a new upper from PSA. The other upper I bought about 8 years ago from someone on another forum. I don't really know any of the details about the upper's origins. Any solution here? I suppose I could put the old FSB back on and then chop it down to just a gas block and hide it under a longer rail, but i really wanted to have a FSB on it (one that works).

Thanks in advance.