Nige,
I don't have the nodal points for that particular lens. But you are correct...the nodal point varies with the mm length chosen at the time of imaging.
Here is a simple way to find the nodal point at anytime at any given focal length.
Shoot an image with a forground object (say a thin tree) and an object behind it and just off the tree (its distance is irrelevant).
Take a series of images with the camera locked.
Take another series with the camera SLID down the pano head (I am assuming you have a pano head or else you can never find the nodal point of a lens
) slightly and do the series again.
Move the camera down and do one more series.
Now, when the distant object is equally distant from the tree on each side of the tree on a series...you have found the nodal point for that particular focal length.
Really simple
...just time consuming.
Try it first with a fixed focal lenght lens to take the variability out of the equation.
Stephen