Don't use any locking substance - you get that lesson driven home when you strip a screw trying to remove it, and have to visit Mr. Gunsmith, and have to have it drilled out.
Proper torque is 20 to 25 inch pounds - but it is not critical. Just snug will do it.
Put a bit of oil or WD-40 in the hole so they won't rust. I have been mounting scopes for~50 years (part of that professionally) and I have never had, or seen, one shoot loose.
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