Here is some more info on the output nut.
I was concerned that replacing what I beleive is a steel nut with an aluminum nut would not allow the aluminum output nut to be tightened enough as aluminum is softer then steel. I did some digging though and found that my concern is probably unwarranted. The torque specs for the output shaft nut in question are 58 ft-lbs. The torque specs on the aluminum yz250 nut are 105 ft-lbs. So the nut should tighten up properly to 58 ft-lbs without issue. I am no machinist so don't take my word on all this though. I guess I will use the aluminum nut tightened to spec and see how it goes. Below is a pic of torqure specs for the KX500 output shaft & YZ250 stem nut.
Here is some more info on this rare output shaft nut:
The nut was used on 74-79 kx250, 79-80 kdx400, 81 kdx420, 82 kdx450, 83-87 kx500 as well as a few other older kawaski models.
If you look on ebay right now there are three of these used nuts for sale ranging from $10 w/ s/h for a crappy one up to $40 w/ s/h for a nice one.
I have found that recently Triumph has used M24x1.0 nuts on there new America & Speedmaster bikes. It is part number t3350680. It sells for $4 new. I do not know what the nut is made out of. I am guessing it is either steel or aluminum. I am gonna stop by the local Triumph dealer and check one out sometime. Here is the nut on line
http://www.2wheelpros.com/oem-parts/triumph-nut-flgd-m24x1-0-t3350680-part.htmlHere is the torque specs on the kx output shaft & yamaha stem nuts.