Well..... Ruger made:
Security Six in both blued and stainless and in 3 barrel lengths so, there's 6 different models.
Police Service Six in both blued and stainless in 4-inch and 2.75-inch so, there's another 4 different models.
Speed Six also in both blued and stainless and in 4-inch and 2.75-inch so, yet another 4 different models.
That's 14 different models and if they made an even number of each you can assume there's no more than about 89,000 of each.
Of course there's always the oddity like some 5-inch guns, a special run for Postal Inspectors that were 3-inch, a few for the NYPD, NIS and even some Speed Six's that were roll marked POLICE Service Six in the factory.
Hope I did my math (and logic) correctly!