Two more differences:
The "2" in the company numbers - the GB the base is curvy but the RIA the base is flat
The "S" in the barrel addresses - the GB the ends are sans serif but the RIA has very pronounced serifs (the squiggly things at the ends of the letter)
I paid under $300 for my Company marked, Colt addressed Armi San Marco Walker last year but of course I did not have all the Italian marking so nicely defarbed nor the finish so well obliterated.
I wonder how many hours went into the antiquing of the GB offering and how much per hour the $1700 more amounts to?
Oh Well, I like mine just as it came from the Bresica factory!