Rick,
It was made in 1919 according to the SN, somewhere along the way it was converted to an AI configuration by the addition of an arched spring housing and extended grip safety, also had an adjustable trigger added.
The man that I bought this one from claimed to be a personal friend of David Harris and had several Colt SAA's engraved by him. I was favorably impressed with the quality of the engraving.
He said that he got the gun in trade on a SAA and it was shiny nickel plated with the plating flaking off. He took it to Harris and asked him to do something with it, this is the result. The parts that are not engraved are a frosty nickel that doesn't show up good in the pics, but really sets off the rest of the gun. It looks much better in real life than in the pictures.
Here is Harris web site:
http://www.dwharris.com/engraving.htm