I can't really help you with the manga.
The novel is about $10 at amazon and it's definately worth reading. It's actually a compilations of three novels written by Yoshiyuki Tomino and is probably what the series would have been if he had full creative control when making it.
A lot of interesting differences, pretty much after Garma dies it splits off entirely and goes in an entirely different direction. For example Amuro hooks up with Sayla
and starts fucking her. The ending is also very different with Amuro killed by a minor character.
It's a pretty good read, you should check it out.