Pre Heresy Legion Organization

Well, I belive that this need a proper thread. I've been thinking in how a legio is structured and organized. There are many holes here and I hope that with your help we can fill this holes.

This is a quote from this topic:
I go for Century [consensus in the absence of a better term for Company divisions].in the Company divisions and organization.
I'm wondering the same about the WE Captains, if they are more or less the equivalent of a Chapter Master, what is the equivalent of a captain? I guess we actually don't have any. But if we go a little forward on time to the Space Crusade/Rogue Trader era --not crusade/pre heresy era I know, is post heresy, I'm guessing the scourge era (or whatever is called) mainly because at least in Space Crusade, there are no Chapters yet, but Legiones Astartes-- We have some nice ranks:

Lieutenant Comander - In charge of ? (not sure about this one).
Captain - In charge of the Company
Lieutenant - In charge of the Century
Sargent - In charge of a squad