I have ran a 4:1 internal mast rotator in my rectangular shaped NACRA boom, and the way I did it was...run all the lines thru the blocks first, then tape the block(micro cheek block) to a batten, run the batten into to the boom until it lines up with the predrilled holes. When its in line, push the rivets in andd squeeze them into place. You must have patience and beer(afterwards, believe me, youre gonna need need it to unwind!) Actually its not that hard, just a bit tedious. A mast seems like a pice of cake compared to the small rectangular boom which already had bungee in it to further complicate matters.