The recruit rank structure is as follows (if memory serves):
RCPO - given symbolic E-7 rank insignia on his collar. He carries the saber and marches the recruit company whenever the Company Commanders direct. Otherwise he marches in the front rank. Also in charge of overall discipline when company commanders are not present.
ARCPO - given symbolic rank E-6 on his collar. Marches in the back of the company to see everything. 2nd recruit in command.
Yeoman - given symbolic rank E-5 on his collar. Writes all watchbills and schedules for entire company. Also writes walking chits for dental appointments etc. (Often a nuke, ET, AT, or FC)
Starboard watch and Port watch are given symbolic rank E-4 and march in the front rank. They are necessary for keeping the company properly spaced during more complex drilling manuevers.
Master at Arms is probably given symbolic rank of E-4 and carries the company's Guidon or flag. Anyway that's my guess, because they called him a guidon bearer when I was a boot. Curiously, the guidon bearer in Marine platoons is the highest ranked boot in the platoon and eventually will be named the company Honorman at graduation.
I am willing to allow that things may have changed in low these many years since this old salt was a boot.