I own a R80 G/S HPN 1986 and ride by far not hard enough to make use of all the benefits the frame bracing is doing.
During a holiday last year I went to see the HPN workshop and had a good look around what they have built in the past and what they still build, and have had long discussions and picking their brains about the frame reinforcement.
They have a full collection of Paris Dakar bikes from 1981 to the oil heads.
The strengthening they do to the GS is to make the bike better putting up with the impact
coming from working the suspension (jumping and corrugated roads).
HPN did actually develop and engineer the frame for the BMW Krauser MKM 1000.and later sold it to Krauser who then started manufacturing a small series. The diagonal bracing from steering head to the swing arm pivot point is designed to minimise the twisting of the frame (high speed direction changing) with putting that in you are improving your frame towards the Krauser style of bike. The collection at HPN includes also at least one of these 'MKM' that is still road registered and gets raced.
With strengthening in the HPN GS way, putting the half moon around the pivot point, and several bracings around the steering head reinforcing the shock mount and foot peg mounts you develop your frame towards a desert racer or around the world mule. If you look at the variety of the sub frames some of them are designed for a light weight rally bike while others are made to mount luggage carrier to it.
is offering a kit of strengthening plates that a guy here in Perth has used to build a HPN relica.The white bike on:http://www.advrider.com/forums/showthread.php?t=787760
the bike with the red frame is a replica of a replica, he copied the SWT parts and my bike design.