A lot of Ruger's production at the very end of the "SIX" series actually had 3" barrels. The postal Service got a bunch of them in the Speed-Six model (the stainless GS-33PS). Would be curious on the sn once you get it, and whether it does have a 3" barrel or not (you can send me a PM if you wish).
A lot of the spurless hammers were put on after factory, so probably won't letter as DAO from the factory. Even "SIX" series guns that are known to have come from the factory with a spurless hammer are known not to letter as DAO
Chet15