Help evaluating my late grandfather's Rolex

[newrolexowner86]

Hey all, I am very new to the Rolex world. With so many variables that can alter the value of these beautiful watches, I am more than confused and turning to you guys for help. What I think I have is a 50's oyster perpetual. It has the bubble back, has "Brevet 6305 1" engraved in it. What I believe to be rare is the fact that it has both "justdate" in red, and the date numbers are all red. I have attached pictures of the watch, as well as a few with the caseback removed thanks to my friendly local (but Rolex illiterate) jeweler. Any help you could give me [edited] is greatly appreciated. Thanks in advance!