Warren Gretz was kind enough to send me replacement 3-3.5 solid rivets which I received on Tuesday. Tonight I had the chance to drill out the two poorly driven 3-5 rivets and put in the proper ones. I then lined things up and tightened the #8 screws to hold everything together. The final step was to use a Scotch abrasive wheel recommended by Gretz to slowly remove just enough of the heated pitot material to fit perfectly in the mast. The only thing left (other than the electrical and static connections) is the nutplates on the access cover itself.