Leo wrote:

Later type KH500 inners offer more rebound damping which is a plus.

You can further improve fork action by reducing diameter of small bore to 1.8 mm and thus increase rebound damping. On top of that, you can reduce compression damping by drilling trough aluminum top of inner rod with 8 mm drill bit.  One should close two of the four holes on the lowest part of the inners.

H-forks have stock springs that are close to OK. Just increase oil level to keep it from bottoming out under severe braking. btw, severe braking is not possible with stock brakes. 

Only if you are way over 130 lbs you will need to change to a stiffer spring.

I have found the 18 inch front wheel to work well up to speed of 100 mph. Past that it becomes unstable. Reduction of triple clamp off-set by 5 mm helps some.   Best thing to do would be to drop an engine into an S-frame. Your worries are over right away.

Per John Aylor:

Here are side by side pics of the aluminum vs steel H2 damper rods.

The recommended modification for the bottom of the steel rod is to weld up two of the four holes and drill the other two out to 1/4".

The damping hole in the side of the rod about 2" down from the top. It is about 5/64" diameter (2mm) and is in the same place on both style rods.  It should be 1.8mm, might be a small hole but the size % difference is pretty big. Almost 20%.

Polish and check after welding to make sure the fork slides smoothly on the damper, as well as the damping parts on the rod after filling the small damping hole.

Pic 1: Steel late model on top with bottom being early aluminum


Pic 2: Same as pic 1 except the items are dissasembled.


Pic 3: Early model aluminum bottom hole close up


Pic 4: Early model aluminum top portion of rod close up.


Pic 5: Late Model steel bottom portion of rod close up.


Pic 6: Late Model steel top portion of rod close up.