How can I know I have been placed into the Body of Christ?
You can know you have been placed into the Body of Christ only because the Book says so. Holy Spirit baptism is not an emotional or physical phenomenon; you never felt anything, and you did not know what happened. It is an unfeeling thing, so assurance rests on Scripture alone.
Les teaches that I Corinthians chapter 12 deals with the Body of Christ, which is composed of people who have been baptized by the Holy Spirit. That Holy Spirit baptism is not an emotional phenomenon and is not a physical thing. You and I never felt a thing, and we did not know anything that happened when the Holy Spirit baptized us into the Body. It is an unfeeling thing, and we know it happened only because the Book says so. That is the only way we know that we were placed into the Body of Christ, and we have to leave it at that. We do not try to look for some kind of emotional thing or a feeling, because the word feeling is not used in Scripture.