Just a little update on this. I'm just finishing up the Colt Armorer Class and I asked the instructor about this topic.

The way Young Manufacturer recommends installing the carrier key is the new way of installing it and it is absolutely acceptable. If you want to stake the key after using the red loctite and torquing it down, you can, but it is NOT necessary. The old way of doing it is to torque the screws down and staking them. BOTH WAYS ARE ACCEPTABLE.

I also asked about the castle nut and he doesn't recommend using blue loctite because it can damage the threads. It will definitely hold it in place, but if you plan on taking the buffer tube off, he does not recommend using using the blue loctite so I won't be using any loctite on the buffer tube.