A: watch the video. B: As stated, the seals are pulled into place. There are grooves machined along the length of the rotors, and the seals are lightly lubed and pulled in from one end, generally grasped with ViseGrips.
I used to run top fuel many years ago and I must admit things have changed a great deal since I raced, but I am curious that you didn't show the procedure for timing the rotors. For those who don't know that is setting the rotor to rotor dimensions to prevent clashing at high RPM. Also the dimensions can be set to lead one rotor over the other if desired.