It sounds as if you are saying that the Son and the Holy Spirit are one and the same.  You said that the Holy Spirit is the spirit of Christ, and that the Spirit of Christ is who came down and indwelt the Church.

 This is not the place to discuss the essence of God as a Trinity.  But the Bible teaches that the Holy Spirit is a distinct member of the Trinity.  He is the Spirit of God , but not the spirit of Christ.  Sounds like "splitting hairs," and I'm not going to try to attempt to explain what I mean by this in this forum.  My point here is to show that it was not the "spirit of Christ" who came down on Pentecost to indwell the Church, but rather it was the Holy Spirit, the 3rd member of the Trinity as distinguished from Christ (the Son, the 2nd member.) John 14: 16, 26:  And I will pray the Father, and He shall give you another Comforter, that He may abide with you for ever.                           But the Comforter, [which is] the Holy Ghost, whom the Father will send in my name, He shall teach you all things, and bring all things to your                           remembrance, whatsoever I have said unto you. John 15: 26:  But when the Comforter is come, whom I will send unto you from the Father, [even] the Spirit of truth, which proceedeth from the Father, he                      shall testify of me. John 16: 7:   Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will                    send him unto you. These verses clearly are saying that it was the Holy Spirit that was sent on Pentecost, not "the spirit of Christ," to indwell the Church.  John 14:16 says that Jesus will send ANOTHER  Comforter, meaning that it won't be Jesus Christ or the "spirit of Christ.  Jesus did nothing on Pentecost (so far) but send the Holy Spirit.  And His mission was to comfort and teach and seal the Believer until Jesus Himself comes on Pentecost to fulfill this Feast by rapturing the Believer. 

As for my question of "Where in the activities stipulated by God for the Feast of Weeks (Lev. 23: 15-22) is there a symbolic representation of the Holy Spirit coming down to indwell the Church?".....you didn't answer this question.  The waving of the two leavened loaves seem to represent the rapturing of saved Jews and Gentiles together as the Church.  I am unaware as to the symolism of the waving of the meat, but this certainly does not represent the descent of the Holy Spirit to indwell the Church.