FWIW...
For checking head bearing preload I've used a method described in the Honda Goldwing maintenance manual. Basically, to check preload after you have adjusted the head bearing or replaced them or have confirmed that they are in serviceable condition, using a fish scale, attach the scale to one of the fork legs underneath the lower clamp and pull it through lock to lock. An acceptable amount of force to pull the fork lock to lock is 3-5Lbs. I've used this method on my other bikes with good results.
To attach the fish scale, I utilize a reusable ty-rap and place it loosely around the fork then hook the fish scale through the ty-rap.
I don't know how much it matters what the head bearing stem nut is torqued to (my experience is usually 20-25lbs.ft) in preloading the head bearing as long as after the stem nut & lock nut are tightened down the result is 3-5lbs. of pull is required to go lock to lock.
And, the front wheel is off the bike when I do the head bearing preload fish scale check.
And this.....
https://wildguzzi.com/forum/index.php?topic=115893.0