Paul,
IF I remember correctly the rear alignment lug could be adjusted on the weapons and that could be adjusted, by the depot level but I don't think that COD will be shooting it anytime soon so you could get away with the minor adjustment yourself or one of your dedicated vol's (especially if he is a TM)
One more thing to consider when you pmcs your tube(s) it does not tell you to clean the upper alignment guide and knowing the tubes haven't been loaded for many many moons now it would be a good idea to clean it and put a very LIGHT coat of grease in it before you load your weapon of choice and IF you were really bored and wanted to make sure that that rail isn't damaged at all or too corroded you can make a mock up guide and lay on your back on the rolling tray if you have one and go from the breech door to the muzzle door making sure that it goes through without any problems and if you do find a problem with it then a quick job with a fine teeth file will take care of the problem.....
Then make sure that you have someone who knows how to roll the stop bolt while you are in the tube (and after it has been greased) and roll the stop bolt to the load position and then to the lock position and then the fire position, IF possible do that two or three times if you are going to completly tube load the weapon that way you know that there is NO way for this thing to come out unless there is someone there who knows exactly what they are doing. And the preservative that is recommended for the tubes is HEAVY mineral oil and not grease, however with time the heavy mineral oil will thicken and turn a green color (we have that in tube #2 and I have been wondering what kind of grease was used to preserve it and the book shows using mineral oil instead of grease, I should have read that chapter a while ago)