Take your trusty dial calipers and measure the distance from the middle of the gas port on the barrel to the shoulder.  Then measure the distance on the gas block and adjust accordingly.  As far as rotational adjustment make a small mark on the barrel right behind the shoulder that lines up with the gas port hole, then line the block up with that on installation.  

I'm not sure how the LaRue fits as I haven't handled one yet, just remember that blue loctite is always a good companion for setscrews.

1) How do I make sure that the gas block lines up with the gas port?

One of the screws on the botton is directly under the gas port hole in the block. Put the block on upside down and watch for the gas port in the barrel to line up through the hole. Now turn it around so its positioned the right way.

2) How do I make sure the gasblock is aligned vertically?

It just has to be close. The gas port hole in the  block is way bigger than the port in the barrel.

3) How do I keep the gasblock from shifting fore and aft on the barrel?

Tighten the screws and shoot it. The carbon build up from any leak in the gas system will seal it in place.



Thanks in advance.