I have never seen a TT pushrod tube "in the flesh" so don't quite see how how they are adjustable other than the smaller section being able to slide up and down in the crankcase seals? Does the the smaller diameter tube slide in the larger diameter part that screws into the head? If so is there a seal in the larger diameter part. A drawing would help explain the setup if someone has one.
The drawing is very helpful. 609 MPH, page 18.
The adaptor becomes part of the head, in effect, and the bottom of the adaptor is angled and flanged to mate with the tube, at an angle, if necessary.
See MPH for the full set of drawings.
David