I put I knew gas block on a 74 that has the front sight integrated.  My thought is blue loctite on the screws but thought I’d get some opinions first.  

The red is high strength and more permanent.

You have to use heat to remove the screws afterward.

as stated above Blue Loctite is removable and red is allegedly permanent. If you plan on removing it again use blue, if not go with red. You could still crack red loose if you needed to but IMHO I’d stay away from the red with smaller threads especially if your thinking of removal at some point down the road. Blue is fine for my needs and has never loosened on its own for me.  Whatever product you use just clean the threads of any oil before applying

I may want to remove so I’ll use blue.  Thanks folks. 

I’d go red.

It is pretty vital that the gas block stays rock solid. I would want to make sure that the block has every opportunity to stay tight and in place.

You can always use some heat to loosen it if necessary to change it later.

Using red will save me a trip to the store and I want to shoot this tomorrow.