This thread certainly has strayed a bit from where the originator had wanted it to go, so allow me to reel it back in a bit.
Here's a photo of another original Chiefs Special Airweight, coincidentally also serial number #278XX.
What's interesting is that unlike ar15ed's, mine is sans the extra bug screw. A lot of collectors presume that the bug screw was a very early feature of the alloy cylinder equipped Chiefs Special Airweight, but from what I have been able to determine, it was in fact something added as production progressed. That we have two guns here numbered so closely together, one with the bug screw and the other without, seems to help nail down a range where the transition occurred.
I also have an even earlier Chiefs Special Airweight, #242XX, for which I don't have a photo as of yet, but it is in all particulars (other than the serial number, of coiurse) indistinguishable from my #278XX pictured above (to be absolutely clear, #242XX doesn't have a bug screw, either, nor a smaller triggerguard).