Danny:
I reckon the K-Birdsheads are getting a bit more collectible.
Those production numbers are available year by year with serial no ranges. HOWEVER----
I was told by the
customer service folks at Ruger that the Birdshead S/N's were not any special series.
In other words, there
might be something like:
First a plowhandle Vaquero numbered as xx123,
then a birdshead Vaquero numbered as xx124,
then a plowhandle Vaquero numbered as xx125,
then a Bisley Vaquero numbered as xx126,
etc, etc, etc.
Just an example.
Mustang Gregg
PS.....Not Gospel. It would be good to ask an expert. Like the Ruger Collectors Association.