Yes, handled one a couple months ago. A great looking rifle!!
The word is that there were 12 made in 1976, and those twelve do have barrels rollmarked with "MADE IN THE 200th YEAR OF AMERICAN LIBERTY". This would be in addition to the prototype you mentioned.
Everybody should know that most of that technical info that was put in R. L. Wilson's book on the M77 (serial numbers and such) came right out of Ron Burkes M77 book. Apparently it is a lot easier for somebody to just "plaguerize" right out of somebody else's effort in order to make the one who did the plaguerizing look really good!! I know, 'cause R. L. did the same with the technical sn and variety information from my book on Ruger's .22 autos.
The sn you quoted that was Robert Chatfield Taylor's is believed to have been the prototype to the model, and its now in a private collection (the man who wrote the M77 book).
I also have 5 of the 12 known Liberties noted with sn's between 71-12189 and 71-12513.
Of course, this info and a whole lot more can be found in the Reference of Ruger Firearms published by Red Eagle News Exchange.
Chet15