First, clean end of tube and hole in block with alcohol or acetone. Apply thin coat of "The Right Stuff" on end of tube. Now, go down from the top. Put a phillips screw driver in the top of tube and gently tap on end of the screw driver handle. Be sure the tab on the tube with the bolt hole is oriented correctly with where it fastens. The issue will then be access to install the tube's retaining bolt.

P.S. If the tube does not want to go in the block hole, I have had to reduce the diameter of new tubes with emery cloth in order to get them to fit.

Hope this helps at least a little.