Nice watch. I'm not familiar with the 2775, could I ask what makes you think this isn't one of the 2447s without tachy scale? Like this one:

Hands look all original, and the dial nicely patinated. Round, rather than bar, pushers suggest manufacture post-WWII rather than before or during. These watches seem to have fairly tightly clustered serials (on the movement), I wonder where yours fits in against those shown on OTD:

http://www.onthedash.com/Guide/_Chronographs/1940s_Chronographs/Reference_2447/