It is hard to hurt Tapered Roller Bearings in a low speed application like this. Make it tight.
Hard for anyone to measure torque on the bearing lock nut, a better way to do it is to measure the turning torque of the triple clamp. A common fish scale pulled tangentially to the radius at the fork mounting bores (clamps) should show a significant increase in torque as the nut first brings the roller bearings into contact with the races, then a slow increase as the nut is tightened and the bearing pre-load is increased.
(We checked high speed spindles this way to insure the pre-loads where within a narrow range.)
Make sure the bearing grease is worked by rotating the triple clamp lock to lock dozens of times as the bearing lock nut is tightened.
If you tighten and loosen the nut a few times as you rotate the triple clamp back and forth you should be able to feel the increase in torque as the bearings seat against their races, then feel the increase in torque as you tighten the nut past this contact point.
I set mine by "feel", IMHO unless you put a big cheater bar on the shock adjusting wrench, you would be hard pressed to make the bearing lock nut tight enough to make them fail, or the steering too stiff... Much more important you insure the bearings are in a pre-loaded (zero looseness) condition.
