I recommend you get the
BSA manuals CD, it has everything on it that you can think of needing. It has parts lists and all the applicable service sheets (no factory manuals for those years). Also, if you have any specific questions, as you've seen, there are a number of people who have nice examples of these machines.
Oh, and, according to the parts manuals, the "Alien Head" cowl came out with the '53 model year.