@Fauxvail: Sorry, I don't have a mirror for this download, just the file here on the forum's space. Have you tried again recently?
@Skullar: Glad you're excited to try the mod! You are correct, in order to advance much beyond the basics of the research tree you will need to pick between Ultramarines Chapter Operations and Imperial Guard Operations, respectively opening up those branches of the research while locking out the other. You cannot switch back on this choice later in your campaign. However, more IG equipment is available from the start of the mod than for the marines, so you still have the option to play the guard in a limited sense if you pick marines, but you won't get much of the new toys that this mod provides.