Sorry, but the physical dimensions of the lens are not related in any way to the location of the first and second principal planes. Those are the points that are used in the optical design.
Specifically, the intersection of the first plane with the optical axis defines the first principal point or "front node", designated H or H1, while the intersection of the second plane with the axis defines the second principal point or "rear node" (H' or H2).
By definition, all rays exiting the lens appear to emanate from the second principal point H2.
When focused on a subject at infinity, the distance from the rear node to the plane of focus is defined as the lens focal length.
The lens nodes are theoretical points, defined during lens design. They have no physical identity, i.e. they cannot be "seen". Consequently those positions can only be measured with optical instruments.
The location of the nodal points are not in any way constrained to be within the physical body of the lens. In particular, with long focal length lenses, the rear node may be way out in front of the lens.
- Leigh