Thank you for your kind words, Ken.
Blade man, the problem is that the only commentaries dating from the period when the gladius was in use are histories and, Polybius aside, seem to think that any reader of the history already knew about its use. Polybius, though, was a Hellenistic Greek taken to Rome as a form of hostage after Rome had conquered Greece and Macedonia. Since he was writing for the Greek audience, he did not assume, and there is much useful information to be found there. You need to be caeful when using later writers, such as Vegetiius, in what they have to say about the gladius, as they were writing during teh decay of eh Empire and were idolizing the weapons, organization, tactics, etc., of the period of greatest Roman expansion.
I will note that the blades on the gladius seem to have decreased in length right up into the 3rd Century, when it was discontinued along with the manipular tactics. For reasonable modern discussions, try:
The Legionary (The Roman World Series), by Peter Connolly
Greece and Rome at War, by Peter Connolly, List Price: $49.95, Our Price: $34.97
Warfare in the Classical World: An Illustrated Encyclopedia of Weapons, Warriors and Warfare in the Ancient Civilisations of Greece and Rome, by John Gibson Warry, List Price: $24.95, Our Price: $17.47.
The latter two are general histories and contain very good discussions on the tactics, weapons, etc. of the various armies at different periods. I recommend both for their general knowledge, Connolly's book being the more academic and Warry's the more basic. The first book is a children's book by Connolly, heavily illustrated, of the early service of an actual Roman legionary during the Principate of Trajan. There is a good bit on his training, including sword and shield practice against a stake, using double-weighted gladius and scutum.